The smaller the dog, the bigger the issue with grooming. Especially when it comes to handling a Chihuahua's feet (or any very small breed; Rat Terrier, Poodle, Pomeranian, Schnauzer, Yorkie). Chihuahua's are very sensitive to the fact that they are small, therefore easily stepped on. These small dogs tend to move their feet out of the way very quickly, and hide them if they fear a painful experience (who wouldn't).
Your approach to trimming your Chihuahua's nails is what will set the tone for the entire experience. If you act differently (talking baby talk, giving treats, or feel apprehensive), don't do it yourself. You should feel as matter-of-fact about nail trimming as you do brushing your own teeth. Your Chihuahua will know (from 10 feet away) if you are carrying any tension or fear, so do not even attempt it until all is calm.
To put your Chihuahua's fears to rest, try these steps: