ok so my friend told me about this and we tried it and got a free meal!
Ok what you do is you go in, act casual, buy a meal, and eat it. after that grip your stomach and sprint to the bathroom. stay in there and just wait for ~2-3 min. Come out and head to the counter and say "Your food made me sick! I demand a refund!" They then will give you you're money back and viola! free food!