General fear:
* Cower: To shrink away from something in fear.
* Flinch: To move suddenly as a reaction to something frightening.
* Startle: To react suddenly to a surprise or fright.
* Tremble: To shake uncontrollably from fear or excitement.
Acting afraid:
* Feign: To pretend to be afraid.
* Mimic: To imitate fear, often for comedic effect.
* Dissemble: To disguise one's true feelings by acting afraid.
Specific reactions:
* Cringe: To recoil in embarrassment or disgust, sometimes also from fear.
* Shirk: To avoid something out of fear or apprehension.
* Run away: To flee from something frightening.
The best word to use will depend on the specific context and the type of fear being portrayed.