Antonin's chuckle seemed to indicate that he wasn't upset by the performance, but Hermione knew him better than that. It must have been maddening for him to be standing upstairs watching the action unfold and unable to do anything. Likely he was only moments away from storming out of the hidden room to curse Alecto and Augustus at the same time. It was an amusing enough thought that Hermione found herself chuckling right along with him. At least they could pretend for the briefest of moments that nothing out of the ordinary was happening.