The Dursleys constantly rant about โmagicโ while Harry is growing up, so young Harry assumes they mean street and stage magicians.
He becomes obsessed with learning sleight of hand and gets surprisingly good at it before Hogwarts.
Harry: Is this your card?
Snape: Yes, it is. How did you do that, Potter?
Harry: A magician never reveals his secrets.
Snape stares at Harry
Snape: Potter, you are literally in a school of magic. Revealing magicโs secrets is all we do here.
Pause
Snape: And 10 points from Gryffindor for your cheek.