So if you're a teacher, you could use this to do in-class demonstrations.
Or if you've got a quiz, you could use this as a poor student's cram mode by putting in the characters you're about to study and cycling through them a bunch of times. Things you get right/wrong won't be saved to your history, but they will go to the beginning/end of the river of words to study, so you'll have to get everything right once before it starts over.
I don't yet know how you'll want to use the scratchpad, so let me know how it works for you, and what else you'd like to see with it.
Try dragging and dropping the words in the river, too, or clicking on a word to jump to it.
Note that you will have to log in to use the scratchpad.
* Internet Explorer won't accept unescaped characters, it seems, but you can make escaped links to them by copying the URLs out of Firefox (but not Safari or Chrome).