A crow in a laboratory in Chicago was given food, but sometimes the technicians forgot to moisten it properly. The crow picked up a small plastic cup that had been given to him as a toy, flew across the lab and filled it up with water, which he emptied onto this food. If he spilled the water en route, he went back and refilled the cup. Crows in aviaries place solid objects in their drinking dishes to raise the level of the water so that they can drink it. Crows in cages have been seen using sticks or strips on newspapers to rake in grain which has fallen outside the cage.
Crows have at least five calls which refer to different kinds of danger.
North American crows understand some, but not all, of the calls made by crows in Europe. The raven, a close relative of the crow, can match different sets of objects based on the number of objects in each set. The birds can count up to six. Like humans in Germany, many crows serve as apprentices. The helpers watch their parents making the new nest and finding food for the nestlings.