Hippos are remarkably agile and aggressive. They occasionally kill or scavenge impala, kudu and buffalo. Sometimes they even kill humans. On nightly sojourns out of the water, hippos trek miles to nibble on tasty vegetation – including crops, making humans and hippos uneasy neighbours. Most grazers rely on sharp incisors to carefully nip the top of vegetation. Hippos do have lengthy incisors and canines but their purpose is combat, not grass mowing. These mammals have to clip grass with their lips.