Getting the prey warm enough is step number one. After that, the most common mistake when trying to convert to f/t is being too eager and shoving it in their face - which is just going to set you back to square one 9/10 of the time. Work that rat like it's alive. Sometimes a break in the line of sight helps to get them interested. If you have a big water dish you can "crawl" the rat around, bringing it just within striking range then back out a few times.