Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is one of those World War II movies where they throw together a bunch of misfit soldiers and turn them into an elite fighting force in only a few months, then send them into combat to do impossible missions - part Dirty Dozen, part Guns of Navarone. It's based on a real WWII Special Forces brigade.
When Colonel Frederick, played by William Holden, is inspecting the run-down building that will become his office at his new training base, his assistant sees a rattlesnake in the corner and shoots it with his pistol. A Major, Vince Edwards, comes running in complaining that they shot the snake. He's been collecting snakes and keeping them in his foot locker to cure his fear of snakes just like he joined the Paratroopers to get rid of his fear of jumping out of airplanes.
Later the Major complains to the Colonel that somebody stole one of his snakes. The new recruits for the new Special Forces brigade are made up of a group of Canadians and a separate group of Americans. The Americans are constantly picking on the Canadians. To show their dislike of the Canadian Corporal, some American soldiers hide the stolen rattlesnake under his bed covers. He is startled to find the snake, but he is not bitten and this snake is not killed as far as we see.
The snakes used are real live Western Diamond-backed Rattlesnakes, as far as I can tell. It's possible the same snake was used for both scenes. The first snake was actually alive before it was killed - you can see it's tongue moving just before it is shot. The shooting sequence was not very well done. The first shot comes from the right of the gun we see and it blows the bags around on the floor. That shot appears to blow the snake's head off. Then the second gun fires. When the Major picks up the snake, it is missing its head, but it also has a body wound. That might have been caused by the second gun.