If you want to experience something similar, put your head under water in a pool or bathtub and have someone speak to you while your head is submerged. (babycenter.com)
This small handheld device is a waterproof camera that allows submerged up to 10 feet under water for up to 2 hours of use. (gadgetfolder.com)
He is much less likely to panic if he has the vest on and doesn't go under water. (okcpetsmagazine.com)