If you run into a gate mouth first, you’re going to have a problem. Smashing your mouth into a gate is going to hurt. A lot. The problem you’re now in is one of getting to a hospital and having your mouth sewn back on. The question is, how are you going to get to the hospital?
The reason you ran mouth first into this gate was because you were being chased by a monster (もん). A monster in and of itself is a big enough problem as is, let alone smashing your mouth into a gate. You poor, hapless soul.