"Twirl" is a variant (chiefly Scottish) of "tirl" (also chiefly Scottish) which means to make a rattling sound. When we were visiting some old fortified houses in Scotland, I seem to recall being shown a device on the outside of a door that was a verticle piece of metal with spiral ridges (a twisted "pin") mounted perhaps an inch or three out. On the pin was a ring that was free to move up and down, so that one could move the ring up and down and produce a rattling sound that would transmit to the inside and announce a visitor...."twirling" or "tirling" the ring, or the pin. .. as we find in so many of the old ballads. My memory is a little hazy, but perhaps others can refine this recollection.

--Judy Cook