4. Dummy being blind and deaf, his partner is not liable to any penalty for
an error whence he can gain no advantage. Thus he may expose some or all of
his cards, or declare that he has the game or trick, &c., without incurring
any penalty; if, however, he lead from Dummy's hand when he should lead
from his own, or _vice versa_, a suit may be called from the hand which
ought to have led.