Steal his pet while he's away
Keep it in your freezer
Help him search for the pet, as long as it takes
Make signs and all that jazz
Wait until he forgets, moves on. A year or two down the road.
Make him stew or tacos or soup, ot doesnt matter really, just a meat dish for dinner or lunch sometime.
Substitute the meat for his pet
Tell him midway, after he says how delicious it is
Show him the rest when he doesn't believe you
Stab through the heart and use him as your next stew for his parents when they go looking for him and you repeat the process