What is this? http://cgi.ebay.com/TROTLINE-TROLLE...goryZ793QQssPageNameZWDVWQQrdZ1QQcmdZViewItem I thought I knew this subject since I am primarily a trotliner. But this one has me puzzled. I do not see how to use them on a line. I know the use for the grappling hooks. I keep one in the boat to retrieve lines that have been cut.