Changelings
Changelings— One Irish belief was that FAIRIES occasionally kidnapped human children and replaced them with a fairy child; this was often performed on Halloween. A changeling could be forced to reveal itself by boiling eggshells in its presence (boiling eggshells would cause the imp to exclaim that in all his centuries of life he’d never seen the like, thus revealing himself ).
SOURCE:
The Halloween Encyclopedia Second Edition written by Lisa Morton © 2011 Lisa Morton. All rights reserved