also if you have done require 'json/add/rails' you are in for fun (https://github.com/ruby/ruby/blob/v1_9_2_381/ext/json/lib/js...)

    irb(main):001:0> require 'json/add/rails'
    => true
    irb(main):002:0> class Foo
    irb(main):003:1> end
    => nil
    irb(main):004:0> Foo.json_create({"x" => "bar"})
    => #<Foo:0x007fc5f3149540>

https://github.com/search?q=require+%27json%2Fadd%2Frails%27...