There are a few reasons why dogs may freak out when you cut their nails. It could be that they're simply not used to the sensation, or it could be that they're worried about being hurt. Either way, it's important to be calm and gentle when cutting your dog's nails, and to go slowly at first until they get used to it. If your dog continues to freak out, you may want to consider taking them to a groomer or vet to have their nails done.