[telephonetemp]

Time when you can fiddle with cards and write down cryptic series of numbers without attracting undue attention is probably scarce.

[mistercow]

The cards just look like you're playing some form of single player game (hence the name). If you had a journal to write in, then with some practice, you could pass it off as idly playing the game while thinking of what to write.

[DanBC]

> write.

How many prisoners have free access to pens or pencils?

(Not snarky, I really don't know)