What is the pattern to the stomach room with the horns?

At first, I thought it was random, but it isn't. After much trial and error through clicking at random, I was able to get the chicken (as well as two other cards from this room):

1. Click the bottom horn twice. You should get two parts of the same creature.
2. If the parts are for the chicken, click the middle horn.
3. If the parts are for the frog, click the top horn.
4. If the parts are for the snail, click the bottom horn.

If the first two clicks of the horn don't yield the same creature part, don't panic, just start over. It took me about 5 tries using the above method, but I managed to snag the chicken and get out of there.