Had a glitch happen kind of like this once on a MP server.

Somehow, some way, a FISH got stuck in our longship. It wasn't actually in the longship, but dragging along just underneath and behind the rudder. We heard the kronch-kronch-kronch of impact and were looking all over to see what we were hitting. Nada. Then my bud noticed this dead fish and when we started sailing again it followed us.

We pulled to shore and repaired (barely made it, we were way out there looking for Leviathans) and it started up again as soon as we were underway. Bro had to restart the server for it to quit.

That fish really, really wanted to be a snack I guess?