Lesson #2874 - Moats

"Halt, invaders! There is poop in this moat! Go back unless you wish yourself to be infected by a likely-deadly disease!"

(invaders begin swimming through the moat to begin scaling the walls)

"Oh, right, it's the Dark Ages, you're all covered in poop on a regular basis. . . . we didn't think this through."

(Actually, some wet moats were also used to farm fish for the villagers, so maybe invaders were just looking for a good fish fry? I'm just guessing here, I'm not a historian.)