A sexual act when anal sex is involved with two partners, can be heterosexual or two males. When the penis is in the anus, the partner that is "catching" farts. Which in return causes a rattle or vibration that tickles the penis that is in the anus.
Mark and his gay partner, Todd are engaging in anal sex. Todd is penetrating Mark's anus, when Mark suddenly farts. This fart is a nice sensation for Todd as the vibration causes a rattle like a Rattlesnake makes.