Humans aren’t the only species that delights in delivering unexpected little surprises to the ones they love. Anyone with a cat is probably well aware of this fact. Dropping its prey for you to find later on your doorstep is an act of generosity—like delivering a furry fruitcake for you to nibble on. But such generosity is not limited to domesticated animals. A 2007 study showed that rats who had been helped by other rats were likely to “pay it forward” when they saw another rat in need. The males of some species of spider woo their mates by offering delectable treats wrapped in silk. (Although some male spiders can be a real Grinch, and trick the female by wrapping up something completely inedible, like seeds, prey that he has already eaten, or a fruitcake.) Vampire bats are known to share blood with the less fortunate who were unable to find prey during their feeding hours. But perhaps the sweetest gift of all is the gift of cyanide, which the male, six-spot burnet moth gives to his mate. Sure, cyanide is poisonous, but the female knows just how to transform it into a substance that keeps unwanted visitors at a distance. Like fruitcake.