Humans noticed that some otters are juggling rocks but nobody can say for sure why they do this. Anyway, this is absolutely mesmerizing what they do!
The scientists came up with different theories. Some of them think that otters do it just for pleasure. They entertain themselves in this way. There is an opinion that otters do it when they are hungry as otters open mollusks and clams with help of rocks. But what is interesting, some otters use the same rock during the whole life! They store it in pockets of skin under arms.