whales prefer one fin over the other, just like humans are right-handed or left-handed. it is possible to see whether a gray whale is left-fineed or right-finned. the fin that has least barnacles is the fin it uses most. this is because the whale likes to dive down to the ocean floor to scoop up huge amounts of sand from the bottom, filtering out small prey animals that live in it. when the whale does this, many of the barnacles on the side that rubbed along the bottom are scraped off. so, whichever side has fewest barnacles is the side the whale prefers to use when it digs up sand.