This code gives you more life out of a flask. When you're playing as Carnby or the girl, drink the flask and watch carefully. When your character's arm goes down before he/she says "Uuhhmm!", hold DOWN for one second. If your timing is right you'll re-drink the flask and heal again. Repeat as necessary until you're fully healed.
Infinite Health From Flasks
When you're drinking a flask, pay close attention. When your arm goes down, slightly before you say ''umm'', hold DOWN for a second. You should redrink from the flask. Use this to fully heal yourself.