"The perfect pet at the perfect price -- guaranteed." Creature Dex at the bottom of the sub, if you want to include "relatively harmless" alien critters in your campaign.
In a high canyon in the mountains, the players find a skeleton in a cage suspended from a pole. A few miles further, they find another, and a third contains a partially rotten corpse. The fourth contains a living man who looks as if he hasn't eaten in days. Turns out to be the local way of punishing criminals.