This space intentionally left green.
per the designer, (http://www.boardgamegeek.com/thread/254256)
A card can not be increased passed its highest value.
(9) When a card is already maxed (via Slip Behind, say) turned to its top damage, how do you then play TWIST THE KNIFE, which says you turn the card to the next highest value? There is, technically, no next highest value.
(We played that the card is unplayable under those circumstances and goes to no effect. You can't create another side to rotate a card to.)
Correct. If the card is at the highest damage value, you are out of luck.
Stange, this question isn't in the FAQ.