It is embarrassing how many people on here can't distinguish the two. An Ankle Pick requires you to have one hand on the opponents head/neck/shoulder as you reach for the opponents cross ankle with your other hand. A low single is where you shoot a single straight on, grabbing your opponents foot/ankle with your same side hand. Then use leverage, usually your head on the inside of the shin to drive their weight over that ankle. It is common for this shot to end with the shooter coming out the back door if the opponent sits on them. If not the shooter will switch arm control from one leg to both arms around both legs to secure the body. Many people mistake that for ending as a double. That is just the end of the move. Weidman's last second takedown in that college match, Couture on Toney are two examples of low singles.