I'm no mechanic but I think I see why.
Had one between my legs a few days ago while pulling weeds and didn't see it until it moved and went under a bush, it was nowhere near that size but got my attention.
Odd you didn't hear the rattle. Being that close to it would have have put it in the defense mode.
I read somewhere that professionals and plumbers etc. use wasp spray will immediately drive them away. I keep some at the cabin for that reason when I am in the crawl space.
I'm usually a live and let live kind of guy but ANY snake around the house or in the yard gets whacked.
We haven't had a snake close to the house in quite a while. The best thing we ever did was get an outside cat. It takes care of the rodents and there is no reason for snakes to come close unless they get lost. We also have a roadrunner that takes care of the little ones and the lizards and it's fast enough to outrun and outfly the cat … so far. That little ginger cat is a freekin' killer.