In Othello, Act 1, Scene 1, Iago uses the phrases “making the beast with two backs” to refer to Othello and Desdemona making love.
In Shakespeare’s time, “making the beast with two backs” would have been a slang or street term for sex, much like “doing the nasty,” “making whoopy” or “the horizontal hokey-pokey.” I’m sure we could play this game all day.
Shakespeare used slang, idioms, fun phrases, as well as what we might call poetic language and certainly his own coinages.
Start to pay attention (maybe you already do) to the kinds of language and phrasings you use at home, in the office, at the bar, etc. Our everyday speech is filled with such bursts of poetry.
Things like: “Three sheets to the wind” or “I turned beet red.” And so on.
In Act 1, Scene 1, Brabantio says “O heaven! How got she out? O treason of the blood!”
This could be, “Oh my God! How could she stab me in the back like that!”
Notice how “stab me in the back” is a common phrase, but also a metaphor. “Treason of the blood” might have been a familiar phrase to Shakespeare, but it’s not to us. Also, we don’t tend to say “O heaven!” but say “Oh my God!” or “OMG!” all the time.
In Act 1, Scene 2, Iago begins planting seeds of doubt into Othello’s mind by telling him that Brabantio “spoke such scurvy and provoking terms against your honor.” Scurvy was, of course, a disease Shakespeare’s audience would have recognized. England’s growing merchant class would have been familiar with sailor’s battling scurvy on the high seas. Of course “speaking scurvy” means little to us today. It might be translated as “talking smack” or “speaking ill of someone.”
A serious scholar (i.e. not me) might be able to tell you which lines from Shakespeare’s plays are fresh and inventive, and which ones would have been considered ordinary language in the late 16th Century and early 17th. It is, however, a comforting thought for writers that Shakespeare was not 100% Shakespeare. What I mean is that Shakespeare borrowed, absorbed, modified, and plagiarized language from other sources. He also invented. In fact, perhaps we can modify what it means to be a Shakespearean genius, not a pure original genius, but something more like a magpie.