It is easy to confuse fear with aggression or anger in cats. These illustrations show the progression of a cat's facial expression and body posture from a neutral emotional state (left), through increasing levels of fear (middle and right).
Reward good behavior with treats and ignore bad behavior - never speak harshly or use punishment
Ask a staff member if you can open the carrier so your cat can adjust to the exam room and explore
Avoid direct eye contact with your cat
Handle your cat with a towel if necessary
Speak in soft, soothing tones but avoid whispering