I start off the activity by quizzing the students on a couple animals. "It can swim. It can't fly. It's a bird. What is it?" (a penguin, of course)
After running through a few of those and making sure the students have the general idea, I put them into either pairs or small groups. If there's a section of the textbook that lists animal names, I point the students towards it to give them some ideas. Working together, the students should think of two animals that they can write hints about. I usually ask them to write two can or can't sentences as hints, with the third sentence as a free sentence for any hint they like. Every student needs to write their group's hints down.
Once enough pairs and groups have finished writing, ask the students to take their papers and quiz the rest of their classmates. If their classmate answers correctly, they write their name in the "That's right!" section, and if they're incorrect, they write their name under "Sorry..."
Feel free to modify the format of the quizzing section to suit your needs. You could have groups pose a question to the class or whatever other format works best.