Marcia Rubin, who works amazing magic with a Panasonic, and found that she also has sharp eyes. She drew my attention to a strange linear lump on a serviceberry in a woodland understory, and I was delighted to see what she had found.
This is the larva of the red-spotted purple, Limenitis arthemis, and it is a masterful mimic of a bird dropping. I noticed that this one, when it apparently sensed that it had been noticed, froze tight. If one wasn't hip to the ways of bird-dropping mimic caterpillars, it'd be hard to recognize it for what it was. And by nearly any reckoning, a red-spotted purple caterpillar in repose is a very unpalatable looking lump.