The Three-Hare Window of Paderborn.

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