Getting rid of flies is an increasingly technical business (I particularly dislike filling a room with insecticide vapour: that stuff can’t be good for people to inhale).
So today’s invention is a new form of fly swatter. This consists of a pistol grip handle at the front of which is tethered a pair of elastic straps.
These are gripped by the other hand and stretched taught. One strap is slightly shorter than the other, so that as the stretching hand is gradually withdrawn, this strap is released first.
Being made in a high visibility pattern, it encourages the fly to react and begin to jump out of its way. In doing so, it will fail to notice the arrival, milliseconds later, of the low-contrast (longer) strap, which it will have just failed to outjump, and be killed by impact with it.
More background which indicates the fly senses air pressure change, rather than visual motion:
http://news.bbc.co.uk/1/hi/magazine/8105232.stm