Since biblical times there have been those who maintained that the hippopotamus could sweat blood.
So, does the hippopotamus sweat blood? No, hippopotamus doesn’t sweat blood. During warm weather, the hippo’s skin does secrete a reddish, oily liquid which probably makes the skin more resistant to water and also possibly protects it from the air. But this secretion is not blood, although it resembles blood in general appearance.
Various circuses with hippopotamuses on exhibit have encouraged this myth and it has not been especially discouraged by the authors of certain natural history books, who have emphasized half-truths for the sake of sensationalism.