Shoulder
The door leading to the moon can be broken down with one’s shoulder. It’s not a very sturdy door to the moon, so it’s quite easy to drop your shoulder and ram it open.
Picture yourself smashing through this door using your shoulder and seeing the moon on the other side. Hear the splintering of wood as your shoulder crashes through the door and feel the impact with your body.
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かた
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"Wow, your shoulder is just like my catapult (かた)!" you hear someone shout. As you turn you're just in time to see a man catapulting through his own moon door!
Now the weird man is inspecting your shoulder really closely and he keeps muttering "catapult powers" under his breath. It's very unsettling, but he's kind of right. A shoulder works just like the mechanism that winds up a catapult.