You may have heard about crabs crawling out of their shells (molting). Crabs grow, but their hard shells don't, so when their shell starts feeling too small, they crawl out of it with a new soft shell that will expand and harden larger than the one they crawled out of.
People find empty crab shells on the beach, and these are often the molts left behind by a growing crab.
But have you ever watched the process? Here's a great video that shows what it looks like as a crab is crawling out of its shell.