How horrible. Imagine being dropped into water, trying desperately to climb up slippery walls and not being able to get anywhere, and feeling that something large and scary is looming underneath you about to kill you. At least in nature, the mouse has a chance.
When I kept piranhas and was a member of piranha forums, some people made these same kind of mice snuff films. It was usually punk kids trying to be bad-*** or weird social misfits.
Anyone who takes enjoyment in these types of videos needs to seek professional help and grow a heart.
Like Kristina said, feeding dead is kinder and safer.