In early versions of Doom, the player would not be able to step over corpses if they were killed by a fast crushing ceiling. Monsters that were killed first and then crushed would properly allow players to walk "through" the corpse. However, if the monster was killed by a crushing ceiling fast enough that no death animation played, and the monster immediately became a pool of blood, players and other monsters would not be able to cross over the pool of blood and would instead have to walk around it.