When Quaid grabs a person as a shield, the person gets shot multiple times, and grits his teeth in pain. The guy is _dead_: dead people don't grit their teeth. Death-type muscle spasms don't cause your face to contort - just your arms and legs.
Well, corpses, especially recently deceased ones, can do some strange stuff. My job brings me into contact with the recently croaked quite often, and I've seen them do some weird things: fart, belch, blink eyes....even grab things....especially when you move them.
Just cos the person was shot multiple times doesn't mean they died instantly. Some people get shot multiple times and survive, but I bet they grit their teeth when it happens. - This movie was the first time I saw Sharon Stone, and I was blown away by her, and am still in love!