The apparatus is a buccal pump. The shark drops the floor of its mouth and flares the throat while keeping the mouth aperture small, producing a steep pressure drop that draws water and prey inward. Recorded subambient pressures in nurse sharks are among the strongest measured in any fish, and the whole strike takes a few hundredths of a second.
Small pharyngeal teeth then crush hard-shelled prey. The barbels at the front of the snout carry chemosensory and tactile receptors used to probe the seabed, and nurse sharks can also pump water over their gills while stationary, so they need not swim to breathe.
The species is mild-mannered but not inert. Most recorded bites follow people grabbing or sitting on resting sharks, and the same suction that empties a crevice makes a defensive bite very hard to release. Coastal habitat loss and fisheries have moved the nurse shark to Vulnerable.