As David said, the constant accessed in whatever class is specified by 
the class...end block you're currently in. Example:

class Moo; MOO = 'hi' end
class Foo; MOO = 'burp' end
class Foo
 def Moo.greet; p MOO end
end
class Moo
 def Moo.bark; p MOO end
end

irb(main):009:0> Moo.bark
"hi"
irb(main):010:0> Moo.greet
"burp"

Constants share this property with class variables.

So, if you want to inject a factory into your class, you're going to 
have to use a different method, or play around with const_set.

Devin