After you've struck at a survivor twice with your weapon they'll go down on the floor, and this is where you can pick them up with balloons - for whatever reason. To get rid of them, you'll need to sit them in a rocket chair, which will blast them off to oblivion. Which is always nice. When seated, you can stick by the chair to make sure it blasts off without being impeded by other survivors, or even use it as bait so you can lure survivors in before whacking them down.