If a cat's tail, including the tip, stands straight up, it indicates that the cat is in a happy, gentle, and friendly mood and is willing to be close to people. At this time, the owner can gently stroke the cat's head or back, which can increase the bond between the owner and the cat.
If a cat's tail is held upright with a slight curve at the tip, it indicates that the cat is friendly and has a strong interest in the other person, willing to get close, but still somewhat hesitant. If a cat's tail is held upright and its fur is standing on end, it indicates that the cat is feeling fear or threatened, and is nervous and uneasy. The cat may also make a hissing sound to threaten or intimidate the other person. If a cat holds its tail upright and curls it into a small mountain shape, it indicates that the cat is tense or preparing to attack.
