Just smile and nod... Wait a while until the sensei comes around and let him explain it again for you.
You can be a bit evil and at that moment ask the sensei "and what if you do it this way?" (explaining what the know-it-all-student explained to you), and than hear what the sensei says about it, and then look at the face of that know-it-all-student.
Afterwards, ignore the one and try training more often with other partners?
Or trying to say "yame" out loud like senseis voice, so the exercise ends and you can practice with another partner