He made sure he looked sincere to a frightening extent, the same look he pulled on Potter when he asked him whether he fainted because of the Dementor. Potter knew this was teasing, just like what a cat would do to a mouse when he was not hungry, so he made the wise move to leave, closed the book he was reading, swished his wand collecting his belongings and tried to walk away. However, Draco was not done with him yet. He shamelessly stretched out a leg, tripping Potter successfully, yet he stood up swiftly just in time to catch Potter, together they stumbled into the nearest bookshelf, Draco braced them both with one hand, the other slipped behind Potter and grabbed his arse as hard as he could.