> Oily rags can ignite spontaneously.

That happened to a friend of mine. He was doing some woodworking and threw a linseed-oil soaked rag in the trash, then went to work. He returned home to his apartment on fire and a bunch of firetrucks blocking the driveway. Linseed oil apparently spontaneously combusts at 120 degrees and generates heat as it dries, so it can cause a fire in normal 70-80 degree weather.