We've been giving Max allowance for the past couple of months ($3/week). Last night, Stephen didn't have $3, so he gave him a $10 and let him figure out the change. After he got it right, he took $7 from his piggy bank and gave it to his dad.
Max placed the $7 down next to Stephen and said, "Here's your revenge."
Neither Stephen nor I blinked because we both thought we had misheard him, and that he had said "change". However, a few seconds later he piped up with "Revenge is the same as payback."
Ah.... needless to say, Stephen and I laughed heartily.