A volunteer at the zoo recently shared footage of Louis scampering across his pen on two legs.
"People are often surprised to hear that despite his appearance of a tough male gorilla, (Louis) hates to get wet or for his hands and feet to be dirty," primary gorilla keeper Kristen Farley-Rambo, said about Louis in a 2015 blog post. "When caught out in a rainstorm, he'll run bipedally across the yard to seek cover, and when he accidentally steps in mud, he'll find a leaf or a paper bag and wipe his hand or foot off until they are clean again."
It's pretty unusual for gorillas to walk upright for long periods of time, Michael Stern, curator of primates and small mammals, told The Associated Press. In the wild they might stand up to reach food or wade through swamps.
The zoo even created a makeshift bridge from a fire hose over an area that chronically floods that Louis tightrope walks to keep out of the mud.
Louis, 18, was born at the St. Louis Zoo and came to the Philadelphia Zoo in 2004.
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