Insertion of Large Objects Into The Penal Cavity?

After watching several disturbing snuff videos, I have one question - How is this possible? I do not understand how objects that I have seen inside the male urethra, such as a Wrench and a Dildo, is humanly possible. In such videos, they are inserted extremely quickly, and I don't understand how this is so. Any information on how this happens would be great - Or if these are completely fake and it's not possible, would make me feel much more comfortable.