Vacuum sealing an animal is a slow suffocation. It's really not as humane.

CO2 makes the animals fall asleep then die from CO2 poisoning(almost the same as suffocation, except it's humane).

Snake constriction has to do with the compression of the lungs and heart, stopping blood flow and killing very quickly. It's not at all the same as dying by having all the air sucked out of you, while you struggle to breathe for however long a rat takes to die from lack of O2(it's not fast, even a human can last up to 5-7 minutes or longer).

Also, if you did vacuum the rat, you'd take a long time to be certain it's dead, or you'd risk it waking up afterwards. So it's inhumane, inefficient, and really.. makes no sense. Either use cervical dislocation, CO2, heck.. even hitting it in the head with a hammer is at least way faster. There's really no good reason to smother an animal.