To invent, you need a good imagination and a pile of junk.
The chainsaw was originally invented by two doctors called John Aitken and James Jeffray in 1783, for use by Scottish midwives. It was used in an operation called symphysiotomy which widened the pelvis if the baby's head was too large to pass through. The procedure didn’t have a very high success rate and was later superseded by the caesarean section. The chain - modelled on a watch chain with serrations along one side of each link and a handle at each end - could be threaded through soft tissue so that the bone could be sawed inside the body. No anaesthetic was used. The chainsaw was also used to remove diseased bone; the idea being that damaged or diseased knees and elbows could be removed by sawing inside the flesh, and the cut surfaces spliced together to leave a stiff but usable limb.
These early hand-powered saws used a back-and-forth action, but by 1830 had developed into the mechanically-driven ‘osteotome’ which had an endless chain, and which became the prototype of the powered saw used on trees since the 1920s.
The major flaw in the first-ever sound recording device was that it could record sound but couldn’t play it back. It was made by Frenchman Édouard-Léon Scott de Martinville (1817-79), who patented his ‘phonautograph’ in 1857, 20 years before Edison’s phonograph. The device etched representations of sound waves into paper covered in soot from a burning oil lamp. The intention was just to make a visual image of the sound, not to play it back, but in 2008 scientists in California reverse-engineered the squiggles to produce an audible reproduction of a voice singing ‘Au Clair de la Lune’ originally made in 1860. This was 28 years before the oldest-surviving Edison recording. Initially they thought the voice must be Scott’s daughter, but then realised they were playing it back at the wrong speed and that it was probably the man himself.
Today, if you invent a better mousetrap, the government comes along with a better mouse.
QI Series K is due to air this September on BBC Two - keep an eye on qi.com and @qikipedia for updates!