The stranger's interaction with Elisa was a bit awkward since they were not introduced formally and Elisa was a bit professional as she entertains the stranger. On the other hand, Elisa was comfortable with Henry since they have been friends for a while already.
D) "They indicate a channel," he said, "where there's none: giant rocks with razor edges crouch like a sea monster with wide-open jaws. They can crush a ship . . ."
You can see the trickery he used by telling them that the dangerous rocks indicated a chanell.