You ate some grains that made you so sick it feels like a knife is stabbing in your guts and all your poop is falling out. This is called diarrhea. Everyone's had diarrhea before, so you should know this feeling by now.
The diarrhea is here. It's happening. And it smells so awful you can't breathe. You have to take some hollow reeds (り) and shove them up your nose and out the bathroom door so you can get some fresh air in you.