What is "beast with two backs"

n. (context idiomatic euphemistic English) Two people engaged in sexual intercourse.

Making the beast with two backs is a euphemistic metaphor for two persons engaged in sexual intercourse. It refers to the situation in which a couple—in the missionary position or standing—cling to each other as if a single creature, with their backs to the outside.

In English, the expression dates back to at least William Shakespeare's Othello (Act 1, Scene 1, ll. 126-127):

The origin of the phrase is in , because it appears in Rabelais' Gargantua and Pantagruel, c. 1532. This was translated into English by Thomas Urquhart and published posthumously around 1693. In contrast, it is believed that Othello was written by Shakespeare in approximately 1603.