“Yeah, someone might slip dragon dung in it again, eh, Perce?” -- Fred Weasley (GF5)
Dragon dung is a useful material taken from a dragon. Dragon dung is sold by the barrel in Knockturn Alley (CS4). This may be related to its use as compost in Herbology. Great for sending to Percy Weasley at the Ministry of Magic as, uh, an example of fertilizer. Yeah, that’s it (GF5).
Other useful materials from dragons are used in Potions such as dragon's blood.