diff --git a/lib/mutant/constants.rb b/lib/mutant/constants.rb
index 9be1e21b..ef4cf6c4 100644
--- a/lib/mutant/constants.rb
+++ b/lib/mutant/constants.rb
@@ -6,7 +6,7 @@ module Mutant
     '!' => '_bang'
   }.freeze
 
-  BINARY_METHOD_OPERATOR_EXPANSIONS = {
+  OPERATOR_EXPANSIONS = {
     :<=>  => :spaceship_operator,
     :===  => :case_equality_operator,
     :[]=  => :element_writer,
@@ -29,19 +29,20 @@ module Mutant
     :<    => :less_than_operator,
     :>    => :greater_than_operator,
     :+    => :addition_operator,
-    :-    => :substraction_operator
-  }.freeze
-
-  UNARY_METHOD_OPERATOR_EXPANSIONS = {
+    :-    => :substraction_operator,
     :~@   => :unary_match_operator,
     :+@   => :unary_addition_operator,
     :-@   => :unary_substraction_operator,
     :'!'  => :negation_operator
   }.freeze
 
-  BINARY_METHOD_OPERATORS = BINARY_METHOD_OPERATOR_EXPANSIONS.keys.to_set.freeze
+  INDEX_OPERATORS = [ :[], :[]= ].freeze
 
-  OPERATOR_EXPANSIONS = BINARY_METHOD_OPERATOR_EXPANSIONS.merge(UNARY_METHOD_OPERATOR_EXPANSIONS).freeze
+  UNARY_METHOD_OPERATORS = [
+    :~@, :+@, :-@, :'!'
+  ].freeze
+
+  BINARY_METHOD_OPERATORS = (OPERATOR_EXPANSIONS.keys - (INDEX_OPERATORS + UNARY_METHOD_OPERATORS)).to_set.freeze
 
   # Hopefully all types parser does generate
   NODE_TYPES = [
diff --git a/lib/mutant/mutator.rb b/lib/mutant/mutator.rb
index 2864fb5e..af651343 100644
--- a/lib/mutant/mutator.rb
+++ b/lib/mutant/mutator.rb
@@ -12,9 +12,9 @@ module Mutant
     #
     # @api private
     #
-    def self.each(node, &block)
-      return to_enum(__method__, node) unless block_given?
-      Registry.lookup(node).new(node, block)
+    def self.each(node, parent=nil, &block)
+      return to_enum(__method__, node, parent) unless block_given?
+      Registry.lookup(node).new(node, parent, block)
 
       self
     end
@@ -52,19 +52,28 @@ module Mutant
     #
     attr_reader :input
 
+    # Return input
+    #
+    # @return [Object]
+    #
+    # @api private
+    #
+    attr_reader :parent
+
   private
 
     # Initialize object
     #
     # @param [Object] input
+    # @param [Object] parent
     # @param [#call(node)] block
     #
     # @return [undefined]
     #
     # @api private
     #
-    def initialize(input, block)
-      @input, @block = IceNine.deep_freeze(input), block
+    def initialize(input, parent, block)
+      @input, @parent, @block = input, parent, block
       @seen = Set.new
       guard(input)
       dispatch
@@ -173,7 +182,7 @@ module Mutant
     # @api private
     #
     def run(mutator)
-      mutator.new(input, method(:emit))
+      mutator.new(input, self, method(:emit))
     end
 
     # Shortcut to create a new unfrozen duplicate of input
diff --git a/lib/mutant/mutator/node.rb b/lib/mutant/mutator/node.rb
index 47f3143d..ba229999 100644
--- a/lib/mutant/mutator/node.rb
+++ b/lib/mutant/mutator/node.rb
@@ -99,7 +99,7 @@ module Mutant
       # @api private
       #
       def emit_children_mutations
-        Mutator::Util::Array.each(children) do |children|
+        Mutator::Util::Array.each(children, self) do |children|
           emit_self(*children)
         end
       end
@@ -125,7 +125,7 @@ module Mutant
       def mutate_child(index, mutator = Mutator)
         children = node.children
         child = children[index]
-        mutator.each(child) do |mutation|
+        mutator.each(child, self) do |mutation|
           emit_child_update(index, mutation)
         end
       end
diff --git a/lib/mutant/mutator/node/argument.rb b/lib/mutant/mutator/node/argument.rb
index d8f25b18..f0c1f439 100644
--- a/lib/mutant/mutator/node/argument.rb
+++ b/lib/mutant/mutator/node/argument.rb
@@ -30,7 +30,7 @@ module Mutant
         # @api private
         #
         def emit_name_mutation
-          Mutator::Util::Symbol.each(name) do |name|
+          Mutator::Util::Symbol.each(name, self) do |name|
             emit_name(name)
           end
         end
diff --git a/lib/mutant/mutator/node/assignment.rb b/lib/mutant/mutator/node/assignment.rb
index fc7ade97..14365a4a 100644
--- a/lib/mutant/mutator/node/assignment.rb
+++ b/lib/mutant/mutator/node/assignment.rb
@@ -39,7 +39,7 @@ module Mutant
           #
           def mutate_name
             prefix = MAP.fetch(node.type)
-            Mutator::Util::Symbol.each(name) do |name|
+            Mutator::Util::Symbol.each(name, self) do |name|
               emit_name("#{prefix}#{name}")
             end
           end
diff --git a/lib/mutant/mutator/node/begin.rb b/lib/mutant/mutator/node/begin.rb
index 4d54b891..42817fef 100644
--- a/lib/mutant/mutator/node/begin.rb
+++ b/lib/mutant/mutator/node/begin.rb
@@ -16,7 +16,7 @@ module Mutant
         # @api private
         #
         def dispatch
-          Util::Array.each(children) do |children|
+          Util::Array.each(children, self) do |children|
             if children.length > 1
               emit_self(*children)
             end
@@ -24,7 +24,21 @@ module Mutant
           children.each do |child|
             emit(child)
           end
-          emit(nil)
+          emit(nil) unless parent_send?
+        end
+
+        # Test if parent input is a send
+        #
+        # @return [true]
+        #   if parent input is a send node
+        #
+        # @return [false]
+        #   otherwise
+        #
+        # @api private
+        #
+        def parent_send?
+          parent && parent.input.type == :send
         end
 
       end # Block
diff --git a/lib/mutant/mutator/util.rb b/lib/mutant/mutator/util.rb
index 14fae2a1..738663f8 100644
--- a/lib/mutant/mutator/util.rb
+++ b/lib/mutant/mutator/util.rb
@@ -6,6 +6,7 @@ module Mutant
       # Run ulitity mutator
       #
       # @param [Object] object
+      # @param [Object] parent
       #
       # @return [Enumerator<Object>]
       #   if no block given
@@ -15,10 +16,10 @@ module Mutant
       #
       # @api private
       #
-      def self.each(object, &block)
-        return to_enum(__method__, object) unless block_given?
+      def self.each(object, parent, &block)
+        return to_enum(__method__, object, parent) unless block_given?
 
-        new(object, block)
+        new(object, parent, block)
 
         self
       end
diff --git a/spec/unit/mutant/mutator/emit_new_spec.rb b/spec/unit/mutant/mutator/emit_new_spec.rb
index 6f6b1394..09e23b34 100644
--- a/spec/unit/mutant/mutator/emit_new_spec.rb
+++ b/spec/unit/mutant/mutator/emit_new_spec.rb
@@ -15,9 +15,10 @@ describe Mutant::Mutator, '#emit_new' do
     end
   end
 
-  let(:object) { class_under_test.new(input, block) }
-  let(:block)  { Block.new                          }
-  let(:input)  { :input                             }
+  let(:object) { class_under_test.new(input, parent, block) }
+  let(:block)  { Block.new                                  }
+  let(:input)  { :input                                     }
+  let(:parent) { :parent                                    }
 
   let(:class_under_test) do
     Class.new(described_class) do
diff --git a/spec/unit/mutant/mutator/emit_spec.rb b/spec/unit/mutant/mutator/emit_spec.rb
index 15932904..5d0b7713 100644
--- a/spec/unit/mutant/mutator/emit_spec.rb
+++ b/spec/unit/mutant/mutator/emit_spec.rb
@@ -15,9 +15,10 @@ describe Mutant::Mutator, '#emit' do
     end
   end
 
-  let(:object) { class_under_test.new(input, block) }
-  let(:block)  { Block.new                          }
-  let(:input)  { :nput                              }
+  let(:object) { class_under_test.new(input, parent, block) }
+  let(:block)  { Block.new                                  }
+  let(:input)  { :input                                     }
+  let(:parent) { :parent                                    }
 
   let(:class_under_test) do
     Class.new(described_class) do
diff --git a/spec/unit/mutant/mutator/node/send/mutation_spec.rb b/spec/unit/mutant/mutator/node/send/mutation_spec.rb
index 4734f670..ed760b8a 100644
--- a/spec/unit/mutant/mutator/node/send/mutation_spec.rb
+++ b/spec/unit/mutant/mutator/node/send/mutation_spec.rb
@@ -168,21 +168,46 @@ describe Mutant::Mutator, 'send' do
     end
 
     context 'binary operator methods' do
-      Mutant::BINARY_METHOD_OPERATORS.each do |operator|
-        let(:source) { "true #{operator} false" }
+      context 'nested' do
+        let(:source) { '(left - right) / foo' }
 
         let(:mutations) do
           mutations = []
-          mutations << "false #{operator} false"
-          mutations << "nil   #{operator} false"
-          mutations << "true  #{operator} true"
-          mutations << "true  #{operator} nil"
-          mutations << 'true'
-          mutations << 'false'
+          mutations << 'foo'
+          mutations << 'left - right'
         end
 
         it_should_behave_like 'a mutator'
       end
+
+      Mutant::BINARY_METHOD_OPERATORS.each do |operator|
+        context 'on literal scalar arguments' do
+          let(:source) { "true #{operator} false" }
+
+          let(:mutations) do
+            mutations = []
+            mutations << "false #{operator} false"
+            mutations << "nil   #{operator} false"
+            mutations << "true  #{operator} true"
+            mutations << "true  #{operator} nil"
+            mutations << 'true'
+            mutations << 'false'
+          end
+
+          it_should_behave_like 'a mutator'
+        end
+
+        context 'on non literal scalar arguments' do
+          let(:source) { "left #{operator} right" }
+          let(:mutations) do
+            mutations = []
+            mutations << 'left'
+            mutations << 'right'
+          end
+
+          it_should_behave_like 'a mutator'
+        end
+      end
     end
   end
 end