I'm reading By Hook or By Crook by David Crystal. It's a stream of consciousness linguistics/ travel book, whose sudden jumps in topic can be a little disconcerting. It's a lot of fun read in small chunks, though. Shakespeare is one of his favorite topics (and it comes up a lot in his thoughts as he drives across Britain).
When Shakespearian actors forget their lines, they can improvise with a passage of blank verse that doesn't mean anything but sounds like Shakespeare. They alert their fellow actors that they're going off script with the word "nub", and "Milford Haven" signals the end of their improvisation. This is a famous (and funny) nub that Crystal quotes, by Donald Wolfit.
"List, I sense a nubbing in far glens, where minnows swoop the pikey deep which is unpiked less pikey be, cross-bolted in their crispy muffs and choose the trammelled way . . . Oh freeze my soul in fitful sleep lest wind-filled sprites bequim the air and take us singly or in threes in mad agog or lumpsome nub, aghast to Milford Haven."
This is probably a better known piece of Shakespeare trivia, but one that I didn't know: you aren't supposed to say "Macbeth" unless you're performing it. It's considered bad luck for actors to say it otherwise; so it gets called the Scottish Play a lot. And if you do slip up and say Macbeth, the antidote is to immediately say "Angels and ministers of grace defend us," which is a quote from Hamlet.