Maybe it kills them because it lowers their body temp a little. Are alligators quite as fussy concerning cooling as these snakes are, I wonder, as alligators have survived many a colder snap in Florida throughout the ages? Other reptiles live in colder places and survive. I am not at all sure that Tylenol kills them because it lowers their temp, just a thought.
Acetaminophen is actually a very dangerous drug and kills lots of people every year. It readily destroys the liver, so much so that its antidote needs to be given within 8 hours of an overdose, and the victim might still need a liver transplant.
Oddly enough, humans are one of the few animals that can take *some* Acetaminophen without being harmed by it.
For cats, however, it is pure poison:
https://www.addl.purdue.edu/newsletters/1998/spring/acet.shtml