So why did the sorting hat sort Harry in Gryffindor instead of Ravenclaws?

Because Harry is not smart.

Why?

Probably because he tried to catch a letter from the air instead of picking one up from the floor.

Because he hadn't realised that the writing in the Half Blood Prince's potions book was the same as the handwriting he spent 5 years copying off.

But the most important reason:

Seamus - Eye of rabbit, harp string hum, turn this water into rum...
Harry - What's Seamus trying to do with that glass of water?

-/-

Harry: I wonder what Seamus is trying to do with that gla—*gets interrupted by everyone else* TURNING IT INTO RUM!

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