You are a scientist who is working in the Black Mesa research facility when, out of nowhere, alarms start going off. During your panic, you see one of the security guards fall into the door of the room you were working in, his handgun slides towards you. Looking back at the door, you see a strange creature, you think to be called a headcrab, start lurking over towards you. There is the door, a vent, and a window overlooking more of the facility in the room.

What do you do?