It is called the "bull-roarer," and is simply a slat of wood on the end of a string, which when whirled round produces a rather unearthly humming sound.

Will the anthropo-geographer, after studying the distribution of wood and stringy substances round the globe, venture to prophesy that, if man lived his half a million years or so over again, the bull-roarer would be found spread about very much where it is to-day?
"Bull-roarer" is just one of our local names for what survives now-a-days as a toy in many an old-fashioned corner of the British Isles, where it is also known as boomer, buzzer, whizzer, swish, and so on.

Without going farther afield we can get a hint of the two main functions which it seems to have fulfilled amongst ruder peoples.

In Scotland it is, on the one hand, sometimes used to "ca' the cattle hame." A herd-boy has been seen to swing a bull-roarer of his own making, with the result that the beasts were soon running frantically towards the byre.

On the other hand, it is sometimes regarded there as a "thunner-spell," a charm against thunder, the superstition being that like cures like, and whatever makes a noise like thunder will be on good terms, so to speak, with the real thunder.
As regards its uses in the rest of the world, it may be said at once that here and there, in Galicia in Europe, in the Malay Peninsula in Asia, and amongst the Bushmen in Africa, it is used to drive or scare animals, whether tame or wild.