Beast with two backs

What's the meaning of the phrase 'Beast with two backs'? Partners engaged in sexual intercourse.

What's the origin of the phrase 'Beast with two backs'?

This modern-sounding phrase is in fact at least as early as Shakespeare. He used it in Othello, 1604:

Iago:

"I am one, sir, that comes to tell you your daughter and the Moor are now making the beast with two backs."

Shakespeare may have been the first to use it in English, although a version of it appears in Rabelais' Gargantua and Pantagruel, circa 1532. This was translated into English by Thomas Urquhart and published posthumously around 1693:

"In the vigour of his age he married Gargamelle, daughter to the King of the Parpaillons, a jolly pug, and well-mouthed wench. These two did oftentimes do the two-backed beast together, joyfully rubbing and frotting their bacon 'gainst one another."

See other phrases and sayings from Shakespeare.