Where they stitch the leather to the rubber.It’s separated it appears the Rubber tore free from the lower Half of the boot. Someone just commented if they were new because I barely wear them as you can see in the picture on the sole. I contacted Columbia they took my information said they’re over 12 months old so therefore they’re out of warranty but if I wore them for six months straight they would’ve fell apart . I live in Michigan I wear them mostly on the weekends.(snowy days) My wife purchased many products from Columbia over the years . I’m gonna put a stop to that