when you are in a boat, if you position yourself on a piston in a correct way and then activate it, your boat will sometimes clip through the floor, or the walls. When this occurs, you usually clip 10 or 13 blocks below the piston. You sometimes will come back up when the piston retracts, but sometimes you are stuck suffocating in the wall, or in a weird place. It killed my mending villager once when I was transporting it upstairs.