Braining, KFC chicken grease, tuna juice, deli cup feeding, take the snake on a car ride (works sometimes!), even washing and drying the f/t pink will often work. The most important thing is keep offering frozen. At some point most every corn will start to take them. Offer food at unusual times of day and night, too. There's no "recipe" that works with every snake, but I try those methods first. As a last resort, scenting with lizard, etc. can work, but it can be even harder getting them off of that scent. I'll usually euthanize/let them die before I'll go to those measures, but when it's time to stop trying depends on the person (and snake involved.)