look up what an IUD insertion is like without anesthesia
Yep. When I got my first IUD in, that was some of the worst pain I had experienced in my life. Felt like I was getting stabbed in the cervix, and the cramps afterwards were so bad I puked. Totally worth it, but I wish they had prepared me more beforehand (said I would feel a "pinch").
An invalid turn would be something like placing a move on top of an already-filled square or outside of the 9 grid spaces. It seems obvious to a human that you can't do these things, but computer bugs have a tendency to do things you don't expect. And yes, passing a turn doesn't provide an advantage, but I listed it because it's still technically cheating.