In reference to the "appendage" on the back of the slide...
From the video: "The tactical locking plate makes cocking easier."
I love how they don't bother to explain the most bizarre feature on the gun.
EDIT: Actually, I'm thinking it's just a thing to help you grasp/rack the slide. Like the "ears" on a VP9. Something had convinced it was some kinda lever/decocker/cocker/safety or something... that did something. Oh well.