Somethings not right about the story.
Practical joke gone awry?
I thought practical joke, too. Sounds like just the kind of thing a team full of adolescents would consider a real howler.
On the other hand, I suppose it is possible that he put the bag down in some tempting place and the thing slithered into it.
Yeah, here's your clue.
When I was stationed out on the Mojave desert one of the things you had to be careful of was the snakes (poisonous variety) coming into ground-level entry buildings and getting into your boots or even onto beds. One barracks rat near the door didn’t heed the warnings not to leave the door open. He woke up with a nasty visitor lying across his feet. I don’t think his feet touched the ground getting out the far door of the barracks and he screamed all of the way. It’s possible to pick up a guest if you leave an open suit case in the right place.