You should have gone when we were at bathroom Katniss. That reminds me, did the tributes even go to the bathroom? Like when Katniss was with rue, she'd say one second and she walks behind a tree and pees. And when the careers were waiting on Katniss. How would she be able to stand it??? She probably cut down the tracker jacket nest because she had to crap so bad!!!
There's that and also when you stand on the buttons you put the cubes on, they get pushed. But when sticking anything else on it it won't be pressed. Which means that only the weight of a body will be able to push the buttons.