Short and Simple:
* Fred's afraid of frogs.
* The frail, furry ferret fears fireflies.
More Challenging:
* Afraid of a frightened, feathered friend, Freddie frantically fled the field.
* The fearless, fiery firefly frightened the frail, fearful frog.
Humorous:
* "Fear not!" said the fearless, fuzzy fox, "For I am not afraid of anything, not even a ferocious, feathered fiend!"
You can even make your own by adding a fun adjective before "afraid" and playing with the alliteration!