Snake oil?

The subject of deer whistles is a difficult one to argue for, although I have found several people quite adamant in their opposition to them. The basic idea is that the small plastic device, when attahced to a moving vehicle, emits a sound which cannot be heard by the human ear but is enough to startle deer and will, hopefully, stop them jumping into the road in front of you - thereby saving you from the resulting accident and preserving the deer's life too. Since it's functioning depends on nothing happening it is had to prove that they work - hence the accusation of 'snake oil'.

I have had a deer whistle stuck on my bike for the past few years and have never hit a deer (several birds and a rabbit, but no deer) but that, of course, proves nothing - their are plenty of people riding around without deer whistles who have never hit a deer.

I can offer the following recent experiences, which encourage me to continue carrying the whistle.
A couple of weeks ago I was heading home just after sunset and suddenly saw a muntjac deer by the side of the road, looking as if it was about to run out but completely stationary. It was so still that I checked the next time I went past in the light in case someone had erected a small statue of a deer there!
Last night I was heading home from meeting friends in Moreton when exactly th same thing happened, except this time there were two fallow deer stood by the side of the road. A mile further up the road there was a dead deer in the gutter, which had clearly been very recently hit by a vehicle.

Maybe deer whistles are snake oil, but any sudent of American history (or anyone who has watched QI) may know that the use of 'snake oil' as a dismissive or derogatory term was coined by the sellers of patent medicines and tonics in the nineteenth century to stop people using the snake oil which was widely used by the Chinese immigrants. It was, of course, the snake oil which was the more effective of the two preparations and actually worked.