My four-month-old kitten mounts and kicks its sibling—what’s going on?

If your kitten is only four months old, it is usually not yet sexually mature, so heat is unlikely. Such behavior at this age is generally not a sign of maturity, though a few cats may show early behavior at four months.

As for the kitten using its leg to mount or kick its sibling, this may be the kitten exploring its own body or engaging in self-cleaning and scratching. Kittens learn to groom themselves, including licking fur and cleaning the genital area, and this behavior is usually normal and not a cause for concern.

However, if you notice other abnormal behaviors or symptoms, consult a veterinarian for further evaluation to ensure the kitten’s health and happiness; the vet can give more accurate advice based on the specific situation.