A turn of phrase used on the Disc is
It's hardly dragon magic, is it?
to describe a situation where the desired action, explanation or other resolution of an apparently vexing situation is easier than it seems.
In other phases of the Multiverse, the phrase might come out as
It's hardly rocket science....
The fact this phrase is entering the public consciousness in Ankh-Morpork suggests that the form of propulsion pioneered by Errol the seemingly mutant swamp dragon is becoming common knowledge - either a dragon breeder has succeeded in breeding back into the Errol line, and has made her discovery common knowledge at Cavern Club shows, or those Moon dragons that came back to Earth following the successful Ankh-Morpork moon mission are thriving on the Disc, and are interbreeding with native stock, or both.