1. Stripes?
   yes - go to 2
   no - go to 5
2. 4 fins?
   yes - go to 3
   no - go to 4
3. Smiley face?
   yes => I
   no => H
4. Fat?
   yes => B
   no => E
5. Fat?
   yes - go to 6
   no - go to 8
6. Teeth?
   yes => D
   no - go to 7
7. 4 fins?
   yes => C
   no => F
8. Teeth?
   yes => J
   no - go to 9
9. Smiley face?
   yes => A
   no => G

Note: some keys are duplicated.
Illustration: Nancy Kett.