Solo: When the monitor goes off to open a door, if the door your waiting
to be opened has opened slightly leaving a small hole, you can do a grenade
jump to get up and get through the door. You'll lose health but skip waiting
for the monitor to return.
Co-Op: If one player stays on the lift you'll be able to go to the centre of
the map and drop down. Normally when you try and do this, you'll die as soon
as you attempt to drop down but if one player stays on the lift you'll be
able to get down by losing a little health. When you drop back down, all the
flood you left alive before you reached the lift will be frozen. You can
shoot their arms off and the guns they are holding will be floating in
mid-air. There will be blue doors down their, you can shoot or throw
anything through them but they'll disappear.