I had read about a guy making turkey calls with shells. I had found some really large marsh clams (or some other clam it looked like to me - not a shell expert) while strolling with the wife one day last year. Grabbed a couple of them for grins. I polyurethaned the convex side to make them tough (and purty them up) and then lightly roughed up the concave side. Got some strikers out yesterday and tried them out. Not much of a yelp, but a really pretty purr- fairly high pitched, but pretty easy to vary the pitch a little based on where I scratch it. Since the purr is my main sound, I am gonna give them a try this year and see if any longbeards like them.