This glitch can be done on single player however it is much easier on co-op or multiplayer.

At the end of wave 4 it is a good idea to open the help room as to get better weapons from the random box, then when the players have around 4000-6000 points at about the end of wave 5 or 6, one player should keep using the random box and attempt to get the MG42, the browning 30.cal or the flame-thrower, which is the best as it has unlimited ammunition.

Meanwhile the other player unblocks the stairway in the help room.

Then when this is done you should go upstairs and the person with the flame-thrower (or other guns ) should try to find this point.

There is a piece of wood leaning in a small corner between the support beam next to the sniper rifle cabinet and the broken wall, when you find this point you must sprint towards it, jump as if you're going to land on the wood and then immediately hold down B to go prone and then you must crouch.

This will activate the glitch and the person in the glitch should face the stairs to guard that area, then the other person should go behind the first and guard the single window.

If this is done right the person in the glitch will notice that the zombies come towards you, but then stop 1-2 metres away depending on how good you did the glitch.

This means that no one in front of you can get you or your team-mate apart from through the window your team-mate is guarding, as the person in the glitch can only be attacked from behind.

This would obviously make the glitch harder in single player as you'd have to guard the front and back.

If this is done well with a good pair of zombie killers me and my mate got to wave 43.