Arm
The moon shines on your roof in the evening and a snake suddenly appears! Wait, that's not a snake, it's your arm, sticking out from under the roof.
Arms really look like snakes in the moonlight. Picture it. Your arm is long and shiny, just like a snake.
わん
うで
None
Your arm is exposed to the moon and the outside and you feel a chill. Where are your clothes? Ah, you're nude, eh (うで)?! I guess it is pretty common to sleep in the nude, eh?
Your arms are nude, eh? That's why they look like snakes, you know. You should be more careful.