A pop-pop boat is a toy with a very simple steam engine without moving parts, typically powered by a candle or vegetable oil burner. The name comes from the noise made by some versions of the boats. Other names are putt-putt boat, crazy boat, flash-steamer, hot-air-boat, pulsating water engine boat. Around the world they may be called Can-Can-boot, Knatterboot, toc-toc, Puf-Puf boat, Poof Poof craft, Phut-Phut, or Pouet-Pouet.