They are trying to frighten you.
Why do kittens hiss a lot in the presence of humans before their eyes open, even if they've never lived in the wild?
Their momma taught them..lol
Idk, instinctual ?
Because they can’t sing and dance.
It's a survival Instinct, the kitten doesn't know that the human is not a predator.
Just interesting detail
And more specifically:
Well, even if they have never lived in the wild, this is
something that they do by instinct. In fact, it is their only way to communicate
since they cannot talk. Most of the time, they hiss because they are afraid and
they are trying to defend or protect themselves by frightening you.