Kittens always hiss the most before their eyes are open – you can see that the hissing after their eyes are open is a little less vehement.
(Most kittens this age hiss; I’ve had multiple litters, and they’ve all done it.)
Katia (black) and Kristi (dilute tortie) were part of a group of outside cats who were being fed by a family. The number of cats kept growing, and so the people who were feeding them asked for help. Katia (about 3 years old) and her mother Kristi (about 7 years old) came to us on February 19 & 20, 2018, both heavily pregnant. We thought for sure that Kristi would have her babies at any moment, but Katia surprised us and had her kittens first, 4 of them, in the early morning of February 25th.. Kristi FINALLY had her kittens in the morning of March 19th. Katia is leery of humans, but Kristi loves to be petted.