He's not obnoxious about it, though. In fact, he never gives us any trouble. Just like a man's best friend Two or three times a year, we'll walk up to his tank in the morning and see two of him. We can't rub our eyes hard enough to make the second one go away. It's his molt.
Lobsters are crustaceans, as are crabs and shrimp.
They have a hard shell that doesn't grow with the animal's body. Just like a snake sheds its skin, Clifford periodically sheds his shell in order to grow in crustaceans, this is called molting. Clifford is able to slide out of that shell, leaving it in tact. Thus, the double image. We're usually clued into when this is going to happen, because a few weeks before, he generally stops eating.