Cohaagen: Well, my boy. You're a hero.
Quaid: Fuck you.
Quaid: SCREW YOU!
[Quaid uses drill machine to kill Benny in the mining machine.]
Lori: They erased your identity and implanted a new one. I was written in as your wife so I could watch you and make sure the erasure took. Sorry, Quaid, your whole life is just a dream.
Douglas Quaid: Okay then, if I'm not me, who the hell am I?
Lori: Beats me. I just work here.
Answer: It's not a stunt double, it's a mannequin (fake head actually) of Arnie, used for the artificial head shot.
Grumpy Scot