A leopard seal's post-canine teeth are elaborately lobed. When the jaws close, the cusps of the upper and lower rows mesh into a sieve with narrow gaps between them. The seal takes a mouthful of krill-laden water, closes the jaws and forces the water out through those gaps, retaining the crustaceans.
This is the same broad solution as the crabeater seal's, though the leopard seal's teeth are less refined and its sieve coarser. Stomach contents and stable-isotope studies show diets that vary strongly by season, location and individual: some leopard seals take mostly krill, others concentrate on penguins, fish, cephalopods and young fur seals.
The common picture of a single-minded penguin specialist is therefore misleading. What remains poorly resolved is how those individual specialisations arise and how stable they are over a lifetime, since long-term tracking of individual leopard seals in the pack ice is difficult and the population size is not well established.