Dede has found these useful when the 40 blade is still not able to get matts out.  You remove the round spiral cover, and use your training and discretion to slowly and carefully remove matted by cutting one row of hairs at a time.  I don't recommend you use these without training.  These are sold for humans to use in barber shop.  Please disinfect and or discard for each pet.  Please check with your state laws for disposal of razor blades.  Basically, I am telling you, that you are liable for using this product in any way shape or form.  ONLY USE IF YOU ARE A TRAINED GROOMER.  If you need