And Some More Answers
There are few things any actor dreads more than dropping a line or "going up" as it's known. "Taking a walk on the Moon" is another. My most memorable at Cal Shakes? I was playing Holofernes in Loves Labors Lost with Dan Hiatt (yes, the Dan of Hair Fame) as my scene partner, Nathaniel the Curate. Both are pseudo intellectuals and my character tended to go off in Latin..............Now, I don't speak Latin. Oh, sure I know a few words, know a few things about it, but actually speak it? Nah.
My character had one particular passage in that tongue which had been exceptionally difficult to learn. I drilled it forever and finally felt I had mastered it till Opening flipping Night when after I'd gotten 2 lines out of my mouth, I dried up. Totally. Completely. Couldn't remember my own name. It's difficult to describe what goes on in my head at times like those but I suppose you could liken it to a dog trying to catch its own tail.....your brain runs around in circles frantically grasping at the tail of the conversation you've just had and your "panic motor" just keeps running at higher and higher speeds....... I grunted (in character of course) for awhile before leaning in to Dan and whispering in a tiny, tiny strangled munchkin voice.... ......"help"........... Now, I'd just passed Dan a really hot potato ("Help you out? IN LATIN?") and to his credit and my undying gratitude he managed to croak back just one word of Latin from my final line in the speech which enabled my mind to catch its tail, finish the speech and get off stage as fast as I could. And nobody ever knew a thing had gone wrong.
Sometimes you can fool'em.
Most of the time you can dig yourself out of it--substitute a word you've blanked on (though the results can be hysterical depending on the word you've substituted -- "Go villan! Fetch a sturgeon!" [instead of surgeon] was one memorable word burger I've had related to me.) and sometimes you only dig yourself deeper and wind up muttering gibberish, until one of your kind fellows puts you out of your misery by saying " In sooth m'lord, methinks he's lost his wit!" and leads you off babbling.
There are also the occasions when you'll drop a line and then have to figure out a way to work it back in because it contains vital information--that's fun too. But if you let it rattle you it can ride you the whole performance--we have to shake it off and move on.
It's funny, but I've not witnessed many major blanks in others while doing Shakespeare, though on one memorable occasion during my second year at Ashland, Oregon, Barry Kraft playing Hotspur in Henry IV pt. 1 (and a phenomenal Shakespeare scholar and actor) went up in one of the tent scenes--I was a guard in the background and watched Barry first forget his lines and then proceed to invent the rest of the text. In iambic pentameter. 10 syllables to the line, 5 beats a line, every other syllable stressed. And the amazing thing was that he didn't stop after he'd said the gist of what his line was supposed to be--he kept going. He didn't just finish his speech, he did the equivalent of a double back flip at the end of it.
Now that was amazing.