Making the beast with two backs is a euphemistic metaphor for two people engaged in sexual intercourse. In English, the expression dates back to at least William Shakespeare's Othello (Act 1, Scene 1, ll. 126âÂÂ127, ):
It refers to the situation in which a coupleâÂÂin the missionary position, on their sides, kneeling, or standingâÂÂcling to each other as if a single creature, with their backs to the outside. The earliest known occurrence of the phrase is in Rabelais's Gargantua and Pantagruel (c. 1532) as the phrase la bête àdeux dos. Thomas Urquhart translated Gargantua and Pantagruel into English, which was published posthumously around 1693.