Massachusetts has rattlesnakes (believe it or not). Very protected. Kill one of those suckers and there is hell to pay around here. If they're a danger to life or property...stomp, shovel, and shut up.
(I'd say "shoot," but this is Massachusetts.)
I guess either the rattler didnt warn the guy by rattling its tail, or the guy is a newbie here..its a pretty obvious sound.
Then again, maybe he woke her up and she just snapped.