Fix some typos.

koans/about_constants.rb

@@ -67,7 +67,7 @@ class AboutConstants < EdgeCase::Koan
   end
 
   # QUESTION: Which has precedence: The constant in the lexical scope,
-  # or the constant from the inheritance heirarachy?
+  # or the constant from the inheritance hierarchy?
 
   # ------------------------------------------------------------------
 
@@ -81,7 +81,7 @@ class AboutConstants < EdgeCase::Koan
     assert_equal __, MyAnimals::Oyster.new.legs_in_oyster
   end
 
-  # QUESTION: Now Which has precedence: The constant in the lexical
-  # scope, or the constant from the inheritance heirarachy?  Why is it
+  # QUESTION: Now which has precedence: The constant in the lexical
+  # scope, or the constant from the inheritance hierarchy?  Why is it
   # different than the previous answer?
 end

koans/about_iteration.rb

@@ -65,7 +65,7 @@ class AboutIteration < EdgeCase::Koan
     result = [2, 3, 4].inject(0) { |sum, item| sum + item }
     assert_equal __, result
 
-    result2 = [2, 3, 4].inject(1) { |sum, item| sum * item }
+    result2 = [2, 3, 4].inject(1) { |product, item| product * item }
     assert_equal __, result2
 
     # Extra Credit:

koans/about_message_passing.rb

@@ -99,7 +99,7 @@ class AboutMessagePassing < EdgeCase::Koan
     # keep in mind you can't call method_missing like that in Ruby
     # 1.9. normally.
     #
-    # Thanks.  We now return you to your regularly schedule Ruby
+    # Thanks.  We now return you to your regularly scheduled Ruby
     # Koans.
   end
 

koans/about_modules.rb

@@ -42,7 +42,7 @@ class AboutModules < EdgeCase::Koan
     assert_equal __, fido.bark
   end
 
-  def test_module_methods_are_also_availble_in_the_object
+  def test_module_methods_are_also_available_in_the_object
     fido = Dog.new
     assert_nothing_raised(Exception) do
       fido.set_name("Rover")

koans/about_proxy_object_project.rb

@@ -6,7 +6,7 @@ require File.expand_path(File.dirname(__FILE__) + '/edgecase')
 # below).  You should be able to initialize the proxy object with any
 # object.  Any messages sent to the proxy object should be forwarded
 # to the target object.  As each message is sent, the proxy should
-# record the name of the method send.
+# record the name of the method sent.
 #
 # The proxy class is started for you.  You will need to add a method
 # missing handler and any other supporting methods.  The specification