Leo is trying to think of a not terrible story to tell her when she says that and throws him off guard. Wait, why would his shell need to-

Actually, now that he thinks of it, the Krang did throw him into a rock pretty hard...

"Is there a crack in my shell?" he asks, reaching back to feel for it. He can just brush it with his fingers when he angles his arms the right away, and he winces as he does. It's thin, so it... will probably be fine! But geez...

"...Tape won't really do anything," he says after another second. "It'll heal eventually... I just have to keep it clean until then so it doesn't rot."

Eugh, gross... And he's in some kind of weird dystopian wasteland, so the chances of getting shell rot are high. Can he die again? Great...