Swordfish are among the fastest fish in the ocean, and now scientists may have found at least one reason: The fish secrete a performance-enhancing grease.

Dutch researchers examining two frozen swordfish discovered that there is an oil-producing gland at the base of the sword, connected by capillaries to pores in the skin of the head. The oil is secreted only on the head of the fish, not on its body.

“This isn’t ordinary fish slime,” said the lead author, John J. Videler, a professor of marine zoology at the University of Groningen in the Netherlands. He believes that this waterproof lubrication may give the swordfish a smooth, water-resistant head covering that helps it achieve impressive speeds.