PHILADELPHIA (AP) — A male gorilla at the Philadelphia Zoo is taking a stand against dirty hands by opting to walk on two legs.

Apparently, 18-year-old Louis is a clean freak.

When Louis has his hands full of tomatoes or other snacks, he walks upright like a human to keep food and hands clean, rather than the typical gorilla stance of leaning forward on his knuckles.

Michael Stern, curator of primates and small mammals, says workers had to install a fire hose over a mud puddle in the yard. The nearly 500-pound, 6-foot-tall primate crosses it like a tight rope to avoid getting dirty.

Stern says it’s “pretty unusual” for gorillas to walk around upright. In the wild, Western lowland gorillas like Louis might do it for a few seconds to reach food or wade into swamps.