Paris (AFP) - There is the riddle of the Bermuda Triangle. The unresolved identity of Jack the Ripper. The enigma of how the Universe developed beyond a quark-gluon soup following the Big Bang.
And then there is the Sheepdog Mystery.
A puzzle that has niggled mathematical minds for years, the Mystery is this: how does a single dog get so many selfish sheep to move so efficiently in the same direction?
The answer, revealed on Tuesday in a journal published by Britain's prestigious Royal Society, is that sheepdogs cleverly follow a simple rulebook.
Researchers fitted highly accurate GPS tracking devices into backpacks that were then placed on a trained Australian Kelpie sheepdog and on a flock of 46 female merino sheep in a five-hectare (12-acre) field.
They then used the GPS data to build a computer model of what prompted the dog to move, and how it responded.
Sheep cohesiveness is the big clue.
The dog's first rule is to bind the sheep together by weaving around side-to-side at their backs, and once this has been achieved, it drives the group forward.
"It basically sees white, fluffy things in front of it," said Andrew King of Swansea University in Wales.