The zoo built a special eight-foot-high enclosure for its newly acquired kangaroo, but the next morning the animal was found hopping¹ around outside. The height of the fence was increased to 15 feet, but the kangaroo got out again. Exasperated², the zoo director had the height increased to 30 feet, but the kangaroo still escaped. A giraffe asked the kangaroo, "How high do you think they'll build the fence?"

"I don't know, " said the kangaroo. "Maybe a thousand feet if they keep leaving the gate unlocked.