Resident Evil Zero/Fridge

Fridge Logic

 * Leeches and leech zombies. Leeches have an anesthetic in their saliva when they bite, so the main characters and the people on the train shouldn't be in pain over them. Leeches are also not acidic, so the leech zombies shouldn't cause that sort of burning to the characters.
 * These things are Marcus's pet project. They form human shapes, have a Hive Mind, and have a mouth on their belly, as opposed to a real leech's mouth (which is at the front end of its body). These ain't normal leeches. All bets are officially off.
 * Rebecca is a medic, but she starts out with no healing items. This is semi-justified for gameplay purposes, though. But it's still kind of stupid seeing as she's The Medic of S.T.A.R.S.
 * As The Dark Id mentions in his Let's Play, zombie sharks. What possible use is there for a zombie shark that a regular shark couldn't do? Why would you deliberately make a zombie shark in the first place?
 * Just to see if it works.