The Paderborn cathedral is primarily a 13th century structure, but the Dreihasenfenster (the Three-Hare Window) was added in the 16th century. Notice that each hare has two ears, but altogether there is only one ear per hare. Here's a poem that goes with it:
"Der Hasen und der Löffel drei,
und doch hat jeder Hase zwei."
[The hares and ears are three,
and yet each hare has two[, you see].]
Via David Singmaster's The Three Rabbits and Similar Puzzles