Hippo yawning, Ngorongoro Crater by David Bygott, details below

Nope, he’s not sleepy: “yawning” by hippos is a threat display, used by both male and female, young and old alike, to show off their massive (and very sharp) tusks.

In fact, their tusks are so sharp, they are able to bite a 3 metre crocodile in half.

The Hippo (Hippopotamus amphibius)
is on the IUCN Red List for Threatened Species as “vulnerable”.
Population trend: decreasing.