Today’s etymological comparison is a bit weird, but one I love. Fallar is Spanish for “to fail” and Flatulent is, well, a fancy word for “farting.”
Both come from the Latin Flare, meaning, “to blow.” A fart is definitely a type of blowing; and failing at something being considered a type of blowing is a common image in languages around the world: think about Bart Simpson, in our own language, saying, That Blows!
The f‑l root makes the relationship clear in both words.
Interestingly, from the same Latin root Flare, we also get olfactory (another fancy word for, “the sense of smell”) and blow itself is the anglo-saxon cognate to flare.