A set of 9 ultra-close-up, striking colour photographs of different parts of animals (for example, a spider's silk spinners; a mosquito's eyes), along with display signs and an answer sheet. I've used these on a classroom wall (where children stick up Post-it notes with their guesses) or website / blog (where they post answers online), and it always generates lots of interest, speculation and debate. Photos are in .jpg format for printing or use online, the choice is yours.