the cantonese language has a slang expression "wu gei bak gei" (often written as 烏忌白忌, "black taboo white taboo") which means someone or something is a bad omen or a nuisance. the phrase originates from the cantonese fisher people, because they claim the dolphins eat the fish in their nets. however, in formal chinese, it should be written as 烏鱀白鱀, with the "gei" originally in olden chinese, meaning dolphins. the "wu" refers to the finless porpoises, which are black, and the "bak", white, referring to chinese river dolphins. these two species often interrupt and ruin the fishermen's catch. as years passed, because "dolphin" sounds the same as "bad luck", the meaning of the phrase changed.