In any event, here's the story again.
Teddy had been squirming and making noises like he was warming up to fill a diaper, but I'd put him on the potty two or three times to no avail, so I had taken to ignoring it, because I figured it might be hours before it actually materialized. Sure enough, when I was in the shower shortly after the arrival of chid care, Teddy welcomed child care with a huge spit up and a full diaper. That's my baby boy. I found the diaper after the shower, when I went to move the contents of the washer to the dryer.
Blood. I think. Yikes. Little fibery dark red things. I showed them to child care, who thought maybe blood, maybe something Teddy ate. We had fed him a bite of banana the day before, which he swallowed and eventually spat up with the cheesier version of the usual spit up. Child care thought perhaps these were fibers he'd eaten off of something. Hmm.
After a little digging around on the web (no, I hadn't had any dairy exposure, and I eat a repetitive and simple diet these days), I called my husband, who thought along the same lines as child care and offered up two possibilities: his red and black wool shirt, and the towel on the couch. Aha! The towel (which does a surprisingly effective job of protecting the couch from baby drool) is red cotton, and does shed fibers that might fall apart the way the ones in the diaper had (yes, I am soooo a mother at this point, I poked at the red bits in the poop).
Mystery solved. Whew. We think.