Figure out what similarities the things have, and it should get more specific the lower you go.
There should be 2 statements in each category.
For example:
1a. has feathers (go to step 2)
b. doesn't have feathers (go to step 3)
2a. swims (Duck)
b. doesn't swim (Hen)
3a. has legs (Lizard)
b. doesn't have legs (Snake)
