The tail of an animal is connected with the spine and is an important organ for maintaining balance. Once caught, it is equivalent to being caught and eaten. Therefore, not only foxes, but also cats and dogs will get rid of conditioned reflex when their tails are pinched.
The tail is the blind spot of the fox, so it is very sensitive. The fox's tail is equivalent to 80% of its body length, which is still relatively long. When attacked, they tend to ignore their head and tail, and the tail becomes a blind spot.