Cats’ tongues may be the busiest part of their anatomy. They lick their coats not only to keep clean, but to regulate their body temperatures, fluffing up the fur in winter and wetting it down with saliva to stay cool in summer.
As cats’ tongues work, they collect flakes of skin, loose fur, fleas and dirt. Cats swallow this debris — which is usually dissolved by stomach acid. Some cats, especially long-haired or older ones, may ingest too much hair to dissolve, and upchuck hairballs. Giving your cat hairball ointment will help him digest the hair he or she swallows. Source: Animal Planet