I just watched this how the other day. I have no idea how real it was. The one guy that they ended up picking to "assassinate" a guy sat in an ice cold tub of water for 2 minutes and didn't show any signs of feeling it. Normal heart rate and breathing and such. For all I know it could have been 80 degree water though and the whole thing staged.
http://www.hitfix.com/starr-raving/b...idate-assassin