I heard Diego-san hiss for the very first time ever. He's usually such a calm cat but last night Theo pestered him past the point of no return and Diego hissed and growled at him.
On the other hand this is somewhat a nightly occurence between Thompson and Theo. Theo will want to play or wrestle and Thompson will be game for a while but Theo's unrelenting nature will eventually push Thompson into a hissing fit.
After Diego hissed Theo away, Thompson came over and lie down next to him as if to say, 'been there.'