You may take advantage of any extra-curricular activities by the other side, but you do so at your own risk.

Deception

You may bid or play deceptively, with the normal risk of deceiving your partner as well as the other side. No player may vary tone of voice, gesture, or tempo with deceptive intent. This is considered the most reprehensible behavior of all, and, if repeated, will lead to expulsion from organized bridge, and ostracism in a less formal setting.