If your cat is not used to it, handling the feet can be very stressful for it. Feet are incredibly important to all of us, especially cats who need them for catching prey and defending themselves. In the wild, a cat with an injured foot would be unable to hunt, climb or defend itself. And a part of the domestic cat's memory remembers this which makes them very sensitive about having the feet touched or manipulated. I make a point of gently rubbing Cassie's paws and holding them while she is relaxed on my lap. This makes it much easier when I need to examine them.