Ah, this sounds very familiar. Pouncer does this whenever a new foster comes in. He's stressed from the change and new smells. He's probably wodnering where the young ones went, and why these new ones are here instead. When Pouncer is confused and stressed, he hisses at the world. Hisses at his own shadow at tiems. Don't worry, they calm down after a bit. Sometimes it takes Pouncer a day and he's fine sometimes a week. Let's see... after Abby came back, it was a hectic week: she went away, two came in her place, she returned. He's still hisses at every movement After Harry got fixed and returned it was a good three or four days before he stopped hissing.

Give those two babies a kiss and spend some extra time with Dylan soothing his worried mind!