Well, the poop falls out of the vent and onto your floor or carpet and in my case, the keyboard and between the keys if you don't have a diaper on it.
Buy, if you do have one on the chicken, then the poop will fall into it and you can wash it later so you don't get poop on your hands like I am right now when I'm typing this.
Actually it just falls in the pouch. My daughter loves taking our chickens in public with their stylish diapers. No one complains. Our favorite cochin hen goes to town with us in the car and goes to the feed store. They look forward to our visit.
They know we are crazy but we buy a lot of feed so they forgive us.