I saw these things for sale in hardware stores in Switzerland and decided to make some for myself. The best wood to use is very sappy pine.
(broken link removed to http://picasaweb.google.com/nutfool/InsideOutCandle?authkey=Gv1sRgCKH54bulyoycRA#)
(broken link removed to http://picasaweb.google.com/nutfool/InsideOutCandle?authkey=Gv1sRgCKH54bulyoycRA#)