Hmmm...but not everything that responds to :clone can be cloned.

C:\>irb
irb(main):001:0> x = 1
=> 1
irb(main):002:0> x.class
=> Fixnum
irb(main):003:0> x.respond_to? :clone
=> true
irb(main):004:0> x.clone
TypeError: can't clone Fixnum
        from (irb):4:in `clone'
        from (irb):4
irb(main):005:0>