When a female cat is in heat, she will cry in the middle of the night. This cry is penetrating. The female cat hopes to attract the opposite sex through the sound. To us, it sounds very similar to a baby's cry or a scary scream. But it's actually just the female cat entering estrus. The estrus period of adult female cats occurs twice a year, and each time lasts for 10-15 days. If the owner does not want to hear this sound, the cat can be sterilized.