Cats are scared of cucumbers mainly because the sudden appearance of a cucumber behind them startles them. The cucumber's shape and green color resemble snakes or other predators, triggering a natural fear response. Additionally, cats dislike surprises and unexpected objects appearing in their environment, especially when they are in vulnerable states such as eating or drinking. This combination of surprise and perceived threat causes the exaggerated fearful reaction seen in videos of cats and cucumbers. Experts also warn against intentionally scaring cats with cucumbers, as it can cause them significant stress and anxiety, potentially leading to long-term behavioral issues.