Based on a Soviet animation my friend showed me. It's about a penguin who asks its friend to watch its egg while it goes fishing, and the friend falls asleep and lets the egg fall into the sea. When the penguin returns, the friend can't bear to tell it what happened, so it replaces the egg with a smooth oval stone. The penguin falls for it, and patiently tends its egg. The other eggs all hatch, except for this one...because, you know, it's a rock.

The penguin doesn't take this well, and tries to get the stone egg to play with the other baby penguins, treating it as its precious child. When winter comes, the other babies are all grown up, and everyone starts swimming away to warmer islands. Our unfortunate penguin cannot bear to leave its "egg" behind, so it tries to bring it with it to safety. The heavy stone weighs it down, and exhausted, the penguin drowns at sea.