68-26-244-235:rubinius brian$ cat kind_of.rb 
p 1.__kind_of__(Fixnum)
p 1.kind_of?(Fixnum)
68-26-244-235:rubinius brian$ shotgun/rubinius describe kind_of.rb 
Sexp:
[:block,
 [:newline,
  1,
  "kind_of.rb",
  [:fcall,
   :p,
   [:array, [:call, [:lit, 1], :__kind_of__, [:array, [:const, :Fixnum]]]]]],
 [:newline,
  2,
  "kind_of.rb",
  [:fcall,
   :p,
   [:array, [:call, [:lit, 1], :kind_of?, [:array, [:const, :Fixnum]]]]]]]

Bytecode:
0000:  push_const                 :Fixnum
0002:  meta_push_1                
0003:  kind_of                    
0004:  push_self                  
0005:  set_call_flags             1
0007:  send_stack                 #<SendSite:0xe9 name=p hits=0 misses=0>, 1
0010:  pop                        
0011:  push_const                 :Fixnum
0013:  meta_push_1                
0014:  send_stack                 #<SendSite:0x111 name=kind_of? hits=0 misses=0>, 1
0017:  push_self                  
0018:  set_call_flags             1
0020:  send_stack                 #<SendSite:0x131 name=p hits=0 misses=0>, 1
0023:  pop                        
0024:  push_true                  
0025:  sret