Maura: This expression could also be linked to magicians.
Harp: Oh, because they have the big robes and their sleeves are very long so maybe they’re hiding things there.
Maura: Exactly. So, magicians perform different tricks, for example, maybe they’re hiding some flowers and they make flowers disappear and then suddenly they make the flowers reappear and they keep it up their sleeve, so they pull out the flowers and impress the audience at the right moment.
Harp: OK. So now, to have something up your sleeve is not literal, it’s more just that you could have some knowledge or you could have some techniques that could help you do something.