There was a scene in the recent TV remake of “The Andromeda Strain” where one of the stricken characters buzzes his own head off with a chain saw in one quick motion. How much truth there is to that one can only guess, because chain saws aren’t terribly light, but in some cases the blade is long enough to be able to reach your own neck without too much effort. And if it can make short work of a small-diameter tree... well, you can guess the rest.
I’m wondering if he maybe placed it on a table while it was running, leaned over and let gravity do the rest.
Although gross --- I wondered the same thing?
I used a chainsaw on an elk once, long story, but it was a lot harder to cut through the meat than you think. I thought it would be easy, but in fact I could go much faster with a regular saw and knife. The blade gets filled with meat and it just stops cutting after the first inch or so, in real life it doesn’t work like the movies at all.