Greta cast about herself till she found a tin of broom polish and offered it to Z as well.
"There's nothing sneaky about being in Slytherin. Being in Slytherin is like having a billboard sign cast over your head saying, 'Look at me, I'm sneaky!' The really sneaky ones go into Hufflepuff, push paperwork at the Ministry for twenty years, and nobody even notices when they take over the world with a requisition form."