At her nudge, Roddy turned to see what she desired, mimicking her in everything she did - he was her perfect follower. Inside he was gleeful, both at having pulled off another prank, and at having pleased Bella. He enjoyed pleasing his best friend in such a way.
Of course none of the other students dared to tattle on them. Who would dare? No one. The other houses feared Slytherin, especially Bella and Roddy, for they already had a reputation for cruelty which far outshone the norm for even their house. Roddy was only biding time in this place, anxious to get out into the real world and leave such stupidity behind.
Roddy saw that the teacher was leaving, probably put the incident out of his mind right away. He pulled his own wand, and nodded to Bella with a knowing grin, awaiting her command.