O is for organ pipe wasp nest. Organ pipe wasps or blue devils are small, solitary blue-black wasps, not offensive to humans, with the tiniest wasp waists I've ever seen. They prey mainly on spiders, sealing their paralyzed bodies into tubular mud daub nests to feed their grubs. When the mature wasps emerge, the old nest ends up looking like an organ pipe. They seem to favor basement window wells, but this one is under a (rusty) wall-mounted air conditioner. It's about the size of my hand.
And O is for olefin, which includes polypropylene and polyethylene, synthetic fibers that are light in weight with outstanding wicking properties. Some cyclists wear polypro socks and cycling sandals in very hot weather because perspiration evaporates faster from polypro than from anything else, even bare skin, so their feet stay cooler. Alas, olefin also retains odors tenaciously, unless combined with metallic silver.
See the rest of my ABCs.