If you touch the root of the cat's tail, the tail will stand up. This may be due to a conditioned reflex or to express friendliness. It means that the cat trusts you and is friendly to you. Generally, when cats are young, the mother cat will help the kitten clean up its excrement, so when the owner strokes the cat near its tail, it will have a conditioned reflex. Cats also use their tails to communicate and say hello, and they can transmit scent to their owners, which will make them more familiar with their owners.