It was really gruesome for what it was actually. The guy right of frame in the background was using a chainsaw which hit a knot or something and the chainsaw recoiled up and sawed his head off. I had to rewind it twice and move closer to the screen.

How would he rig a chainsaw to malfunction to pop up and cut this guy's head off? I think you're putting too much into the theory that Sidney is some kind of mastermindthere are too many things out of his control to support this.

Sidney could have rigged the chainsaw to kill him.

He was using a chainsaw to cut the wood, it kicked back and cut into his neck, cutting his head off.

I missed it too. I thought the guy in center frame would get hurt.
Did the guy who did die get his head cut off? It looked like something was wrapped up and sitting on the body that was put in the ambulance.

As usual, I was looking at the wrong place and missed it! I was watching the special effects guy's big head!

Chain saw I think