I’m not sure what I’m doing wrong. Seems like I follow the instructions. I’ve tried doing it with a crochet hook and also the version on Knit and Tonic doing a long tail CO with the waste yarn over the thumb and the main yarn over the index finger. But the problem is my cast on never “unzips”. I can tug at the waste yarn or the slip knot or whatever, it just stays put. Any idea where I’m going wrong?