Narrator: Across Africa, hippos are ranked among the most dangerous of animals.
They can be unpredictable, and eager for battle.
They don't often back down from a fight.
And yet, they do have a sensitive side.
It's their skin.
And when it comes to skin care, they need a little help.
Unable to pick up a stick and scratch their own backs, they've gone into partnership.
Meet the barbel, a hippo's best friend.
Often, a hippo is trailed by shoals of these loyal little fish.
They even consume the hippo's droppings as they follow.
Once the hippos settle in a comfortable spot, the barbels get to work nibbling away all the ticks and other skin parasites.
It's a bit like a spa treatment, complete with facial and full-body exfoliation.
It seems to lull the hippos into a kind of docile trance.
The barbels' service even includes dental hygiene.
Thanks to the food stuck to the hippo's teeth, these industrious fish are able to feed on exotic vegetation from land which would otherwise be completely out of their reach.