First off go to a revive perk machine. Remember this glitch makes you pretty much have god mode on because you will never have to get the revive perk again! This doesn't work with 2-players.

HERE IT IS:

1. Go to a revive perk machine.
2. Throw a grenade at any part of the machine.
3. Walk towards the grenade and press RB to throw it towards a wall or plain nothing.
4. Then instantaneously get the perk. Do this as fast as you possibly can, the faster, the more better it will work.
5. You did it! Now every time a zombie kills you, you will automatically go down then get back up again unlimited times!