A nart is when you think you had a shart, but then you check, and it's not. If you don't check, then it's not a nart. That is, if you don't confirm that it was Not a Shart, then it cannot be a Nart. It is both a verb and a noun. And is perhaps most comply used as a verb in the past tense: "narted".
I was shopping at Home Depot and pushed too hard to get a fart out and was sure I had sharted myself, so I went to the bathroom to clean up, and it turned out it was only a nart. Thank god.
OR
I narted at Home Depot the other day.
OR
I really hope that was a nart.