After 10 years I finally was successful with stopping the hissing when Patches comes back from the vet. I had tried the towel thing before and Alice would still hiss at Patches for 2 or 3 days when he came back from the vet. Today I had taken a shower right before I took Patches to get his mouth checked after 2 extractions. I used that towel that was still damp and I am sure had a lot of my scent on it on both cats and there was no hissing. She was cautious and smelled him all over but no hissing. I guess it was the combination of my scent with both cat's scent.
