Swordfish do much of their hunting in cold, deep waters where they often search for fast and highly maneuverable prey. In order to improve their visual ability in these conditions, Swordfish will use the muscles that help move their eyes to also heat up the blood flowing around their brain and eyes. Scientists have been able to demonstrate that this can improve their visual processing up to 7-10 times what they would be capable of at ambient temperatures.
Sketch contributed by Victoria Farrar. Fact contributed by Adrian Perez.
Source: Fritsches, K.A., Brill, R.W. and Warrant, E.J., 2005. Warm eyes provide superior vision in swordfishes. Current Biology, 15(1), pp.55-58.