I found this piece about Bull roarers on the web, and thought that the information would be of interest to others as well.
Museum Number: 506
Artefact Name/Title: Wind/Bull roarers, Two plates approximately 9″ x 2″ pierced at one end. Shallow carving of a spiral design on one and angular design on the other. Used for summoning spirits or raising spirit power.
Brief Artefact Name: Wind Roarers
Museum Classification: Working Tools
Information: When a west country witch wishes to draw to her spirit forces when working in the open countryside, she makes use of a wind roarer, being a flat section of shaped hard wood secured to a length of stout pliable string which is then rotated at arm’s length at speed around the head. The sound emitted varies in pitch depending on the blade size and speed of rotation. By this means strange wailing sounds can be created. Little wonder that the spirits come flocking in to see what all the ghastly moaning is about.
With thanks to Hannah Foxe who kindly gave permission for us to use this material from the Folk Museum website.