Do monkeys mind poop in their food?
In the 1950s, scientists discovered that rhesus macaques in Japan washed their food before they ate it. Recently, other studies have tried to determine if the monkeys really care if their food is dirty. Experimental methods included rolling sweet potato chunks in sand, and placing wheat grains or peanuts on real monkey poo, or fake poo. I won't give away the ending, you should read about it yourself!
Some birds prefer love over food
A study of great tits in the UK tagged different bonded birds with RFID chips that could open a feeder. Some bonded pairs of birds could open the same feeder, and eat together. Other birds' chips forced them to eat at different feeders. These birds spent less time at feeders, and were more likely to try to "scrounge" food from their partner when possible. Read more here.
Some birds love to steal food
Ducks find some of their food by diving and bringing mussels up to the water's surface. Scientists observed that when large groups of ducks congregate, gulls come along and steal snacks from the ducks. Gulls can't dive and get mussels without this "help" from the ducks, and the arrival of the ducks to this area in the winter significantly changes the composition of the gull diet.