As a newbie to this sport so much of what I have been reading regards FF is all new to me. One of the many things I need clarification on concerns 'stimulators'. I get the impression that this is a fly that does not mimic any particular insect but is used, as the words suggests, to stimulate a fish to investigate and perhaps strike. Would someone please enlighten me as to just what a stimulator is, how it does what it does and how, when and where should one use it?