The animal's face and body become tense. The ears are held alertly and the pupils constrict. Blood flow is actually shunted away from organs and toward the muscles and brain. The animal is set to react. Most owners have probably witnessed at least some aspect of this reaction in their cat or dog.
Some dogs are horribly afraid of thunder.
Others may be frightened of a visit to their veterinarian. Some cats react very strongly the presence of a stranger in the house. Regardless of the source of the fear, an experience with a panicked pet can be very difficult for an owner. An owner can assume that a hurricane will cause anxiety or panic in their animal. Preparation is the key to keeping the animal as comfortable as possible during this period.