Oh, now you're asking... I really have no idea, but I was test stitching a piece of thin faux leather (actually cut from a Moleskine notebook) to some 2mm cow when that horrible crack noise occurred. We tested it on some scrap fabric afterwards and everything seemed to be working fine, but I'll never forgive myself if I've broken something internally that she discovers at a later date. I don't think I was going too fast, I think it was just a case of me trying to make it do something it wasn't designed to do.