Whale Shark Anatomy
In contrast to what some people belief, whale sharks don't have big sharp teeth, like other sharks do. In fact, the size of their teeth is considerably smaller since their teeth serve no real purpose in feeding. In other words, whale sharks don't chew their food. Being filter-feeders, whale sharks have a unique raking mechanism attached to the insides of their gills that function to filter food from the water they gulp in. Filter-feeding involves a rather interesting, if somewhat odd, logic.
Instead of preying on fishes, a whale shark sucks in mouthfuls of water rich in planktons, macro-algae, and tiny fishes. Then, it closes its mouth to trap the water inside, which is funneled through the gill flaps, where water is expelled. Most of the food particles are trapped against the dermal denticles lining the whale shark's pharynx and gill plates. The gills have fine sieve-like contraptions that are used to sifter planktons. The filters, only 2 to 3 millimeters in diameter, prevent anything other than water and smaller food particles from escaping.
Any organic material that is caught between the gill filters is swallowed in after. To a human perspective, the concept of filter-feeding would appear quite problematic. You might find it hard to understand using your mouth like a sponge filter and swallowing the dirt that accumulates inside the filter. Though whale sharks are quite well experienced at filter-feeding, the difficulty of it is not lost to them. Whale sharks are often reported "coughing," unable to swallow all the food particles trapped in the gill filters. In time, the leftover particles there accumulate and block the filters, making it difficult to eat without coughing and, possibly, choking.
Whale sharks are very active feeders. Unlike other species of sharks, or fishes for that matter, whale sharks rarely stop eating. Since filter-feeding also doesn't require them to chase for food, whale sharks can simply gulp in water even when they are resting in stationary position.
Other Filter-feeder Sharks
Among all species of sharks, two others are filter-feeders: the megamouth shark and the basking shark. The basking shark doesn't filter-feed the way whale sharks do. Instead of gulping and expelling water through their gills, basking sharks simply "basks," thus forcing the water to flow through their gills. The food particles are then collected and swallowed.
As it turns out, whale sharks are very different from what you first thought them to be. They're filter-feeders and have no use for teeth, much less for a mouthful of sharp, pointy teeth.