Ruby -- or more precisely, MRI, though some other interpretations may do something similar -- uses the a fixed set of object_ids (which is what is stored on the stack to locate an object on the heap) for small integers, so if the object_id is within that range, the interpreter uses it directly to calculate the value, and doesn't need to go to the heap to get a value. (MRI does a similar thing with the values nil, true, and false, as well.)
