This little prank was a part of the evening's entertainment. As far as the victim knows, the goal of the exercise is to see how well he can do at chopping a couple of wine corks with a machete while blindfolded. As an added complication, he is first made to take off his shoes and socks and place his feet in a tub of water. (I'm not sure what the excuse is to get him to do this, but the reason it's done will become all too clear.)
The shoeless, sockless, wet-footed victim is blindfolded and handed a machete. A couple of corks are laid out on the chopping blocks in front of him. Helpers are on hand to help him line his machete up with the corks, and he starts taking swings at them, one swing at a time, with repositioning assistance in between chops. (The helpers are also useful for chasing the corks around the stage when the victim wings them with the knife.)
After the victim takes a few whacks (with varying degrees of success), one of the helpers carefully and quietly replaces the corks with the victim's socks. To enthusiastic encouragement from helpers and audience, the victim continues whacking away at the block, shredding his own socks to bits.
The prank worked well, but there was a casualty other than the victim's socks. See how Helper Two's hand is bleeding? Our hapless Victim got a little bit eager with the machete while Helper Two was adjusting the socks on the block for better results. Fortunately the damage to Helper Two's hand was minor.