Once you've got a continuation object, calling it as say (cont 123) is like a C code longjmp(jbuf, 123). It's a jump back to the original call/cc point, and the return value from the call/cc is the 123 in the invoking call, just like setjmp returns the value passed to longjmp. In Scheme of course any object can be "returned" in this way (and even values? for more than one object), not just a single int.

setjmp/longjmp 類比的 call/cc