Skin
Slide down a branch and your skin will come off. Unlike what Tarzan will make you believe, you can't just slide around on branches, they're rough and painful and if you do it your skin will come sliding off and it will hurt.
Imagine sliding down a slide made of a big, branch. The branch's bark digs into your skin and pulls it right off of your body.
ひ
かわ
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Without your skin to protect you, you feel the full heat (ひ) from the friction of your body going down the branch slide.
Your skin protects you from really feeling lots of heat. It gets burned before you and it has many tiny layers to keep you safe from heat generating things like the sun. You really need your skin!