A sex move when the two partners connect bum cheeks and then proceed to defecate into each others anus; if only one person defecates then it is called the Subway train, although if both partners decide to poo, then it is the Subway train collision.
When one sexual partner connects the rectum hole with another, and either one eject's feces into the other's rectum. The other partner, who has received the feces, will excrete it back into the partners, along with her own. This will happen back and forth, making the BulgarianSubway Train
