Authors:

If the actor points a fake gun and pulls the trigger, and you have to fall to your knees, you really do have to sell it. Otherwise, it takes the viewer out of the moment.

"Brains, Blood, and BBQ: Welcome to Greg Nicotero’s Zombie School". Interview with Michael Mechanic, www.motherjones.com. March/April 2014.
If the actor points a fake gun and pulls the trigger, and you have to fall to your knees, you really do have to sell it. Otherwise, it takes the viewer out of the moment.