It seems holding in your fart will force it to come out of your mouth.

Farting’s a reality of life, whether you want to admit it or not. In fact, the average human lets loose 14-16 times a day. Oh, and if you think pulling that pucker string and fighting helps the situation…you’re wrong. It still has to go somewhere. Scientists have found that the misdirected gas then gets absorbed back into your bloodstream. From there, it just has one other place to go: your mouth. Now, you might have a clue as to why that certain someone in the office has breath that smells like ass.

Source: WTHR