1. When did the contestants start screaming out the letters?

2. How does Pat know how many letters are in each puzzle? (are they written on his card?)

As far as contestants "screaming" out the letters? Since 1975 to the best of my recollection.

And as far as I've been able to tell, Sajak either has a card, which shows the letter frequency of the puzzle being played, or perhaps there's a cue card off stage that he views. Most likely he's holding a card which has the information on it.

Regards,
Bill McD.

To answer the second question, there's a stagehand off to the side at a little portable table who holds up the number of fingers for the number of letters. No, when there's just one letter he doesn't hold up the middle finger, although it would be funny to hear what Pat would say about that.