I reached his vet. He told me to give him LOTS and LOTS of fiber tonight, but not to overfeed. (??Didn't really say how much to feed him.)
I mashed a banana into a cup of high-fiber cereal and fed him some. I'll give it to him again in 15 minutes or so. His vet said that usually dogs pass things like this with no problem. I just have to keep an eye on him & his stool for signs of trouble, and be ready to take him in if he gets distressed.

I just talked to his vet last week, and we've been working on changing how I feed Sherman because he's gotten into the habit of inhaling his food. So now I only feed him a small portion, but several times a day. I think he was just plain hungry. I also just found a chewed up empty bag of Yummie Chummies under the table. It was half full earlier tonight. This is the first time he's ever chewed anything up like this & ate it.