The knight in a regular chess set always has the same "look", whether it's attacking, about to be captured, or just languishing in a corner doing nothing. Even when you buy a novelty chess set where the pieces look like real people, each piece always looks strong and confident from beginning to end,
even as its side's army wanes.
I propose a chess set where all the pieces come with two or three replacement heads, so you can update their expressions as the battle progresses, or as you see fit.
(When killed, you could even leave the pieces' decapitated heads lying around the chessboard)
Computer chess games could easily implement this, and it would be both fun and useful for beginners. Chessmen could look angry when they were about to attack, smiley just after capturing something, and scared if they were being attacked. If left in their starting positions unmoved for too long, they would become visibly sleepy and bored, occasionally yawning. This would emphasize the need for the player to develop the pieces as early as possible.
The computer must analyze whether the attacked piece really is in danger, based on whether it is also being defended or not and also based on its value, so a pawn being attacked by a queen but defended by another piece would get the confident look, not the worried look. This would prompt the beginner to ask himself, "Why is that piece so happy?"