Farts usually expel in rhythmic timing according to the laughs. It's like unintentionally playing an instrument.
Yesterday at school I was holding in a fart, and my friend passed me a note that made me giggle, and I lost control for a second and blew a huge one. So then I started laughing even more and I farted even more and I had to run to the bathroom laughing and farting and the whole school was watching me. Traumatizing.