Folders can get gummed up. Pocket lint and dust can accumulate and slow things down. Once in awhile I give my users a bath in hot soapy water. (think Dawn detergent,) then using a pipe cleaner and old toothbrush, followed after rinsing by a hair dryer set to low. A couple of drops of your favorite lube like Tuf-Glide can help to smooth things; and food-grade mineral oil is good if the knife is used for any food prep.