"Any sufficiently advanced bug is indistinguishable from a feature." - Kulawiec, Rich

"A Thaum is the basic unit of magical strength. It has been universally established as the amount of magic needed to create one small white pigeon or three normal sized billiard balls." - Pratchett, Terry in 'The Light Fantastic'

"People who used magic without knowing what they were doing usually came to a sticky end. All over the entire room, sometimes." - Pratchett, Terry in 'Moving Pictures'