According to the article, Fart molecule could be next Viagra published in New Scientist, rats injected with an enzyme that produces hydrogen sulfide in human penises caused erections in the randy little critters. Hydrogen sulfide (H2S) smells like bad flatulance and rotten eggs.
Hydrogen sulfide relaxes blood vessels in the same way as Nitric oxide (NO). Erections occur because the arteries relax and allow blood to flow into the erectile tissue (corpora cavernosa).
What will they come up with next?