I often think that they are like another, separate animal all of their own. Especially the boys. The girls, whilst still docile, are a bit more feisty and do hiss if they are put out by another cat. My boy cats can't physically hiss. One of them has never done it in the 8 years I've had him and the other one made an attempt at it, once and all that came out was this 'ehhhhhhh' sound 