We have already seen that chimps do not take very long over coitus; a number of other mammals are even swifter. Slijper has noted that bulls, rams, and stags copulate "with astonishing rapidity" and that the whole process lasts no more than a few seconds. Horses manage a few minutes. Whales too are said to copulate very rapidly, a circumstance no doubt conditioned by their ungainly mass. In some descriptions of whale coitus the great beasts are said to dive, then to swim towards each other at great speed, "then to surface vertically and to copulate belly to belly." In this act it is often the case that the entire thorax and part of the abdomen protrudes out of the water. Slijper reports eye-witness accounts of such whale copulations. Horizontal copulations in whales is also described, a mode allowing coitus to last up to 30 seconds.