A clonk is what you hear when Margie hits you over the head with her big fry pan :ROFL sorry couldnt resist.
But a clonk is an ancient Europian tool that stimulated the Wels Catfish into biting --- go to catfishconnection.com to see one and search clonk.
Now how do you use it and what does it sound like,,,well you know what it sounds like when you drop a round peeble about the size of a golf ball into the water The kadoup sound is the first then there is the swish from pulling the handle thru the water.
So does it work,,,obviously yes,,,you see ancient europian cave men selling car insurance nearly every day on TV so they had to have had catfish to survive into modern day. [smilie=lol_xtreme.gif]
Do I have one--yes, do I use it yes on occasion, does it help,,,I dunno, I did catch that 63lb flathead in my avatar while using it and several other flatheads last year. Go ahead

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Denny Halgren is the patent holder of this novel tool. You wont find a better individual and more knowledgeable person of flatheads anywhere. The sound the clonk makes is suppose to be very similar to the feeding sound of a Wels cat,,,an old world catfish closely related to our flatheads in North America. Channel Cat and Blues are considered new world cats and althou feed more similar to the Wels feeding style than flatheads do, but improved catch rates with them while using the clonk hasnt really been shown or proven,,but for some reason it does seem to help and work with flatheads.