These curious gibbons were wondering about this strange contraption left in their enclosure. After some tapping and pulling, they realized that it was a box full of treats!

This is what the uploader had to say about the gibbons: “Pilla and Palle got very excited about this item. The juvenile gibbons really enjoyed their enrichment provided by the keepers and volunteers, and had lots of fun discovering the fruits inside the paper box full of grass.” Credit: Polish Dr Dolittle via Storyful