ResEdit 2.x 

Hold down Shift, Option, and Command as you choose "About ResEdit."

You get the chance to enter "pig mode" (oink oink oink). When you put ResEdit into pig mode, resources will be compacted and purged each time ResEdit goes through its event loop (several times a second).  (However, since this makes ResEdit slower, it's not of much use outside Apple.) (Contributed by Ian Neath. (Info about "pig mode" from Chris Webster and Russell Street.)

Mr. Street adds that if you turn on pig mode while running ResEdit from a floppy disk the disk will "oink" a few times each second (most easily heard on an old Plus in a quiet room), but when I tried this my machine crashed.  ;)

Also, just try holding down only command and option as you choose "About ResEdit"...

... to get some credits. (as in who made ResEdit, not as in Star Trek money)