Does the use of special interrogatories without explaining their purpose to the jury confuse the jury?

Thom contends that the use of special interrogatories without explaining their purpose to the jury was confusing, as evidenced by the jury's deadlock on two of the counts. The defendant did not object to the use of the special interrogatories and even acknowledged that the jury's finding would simply be "an advisory" one because the determination of quantity was for the court. Thus we review the district court's actions for plain error. See United States v. Olano, 507 U.S. 725, 733 (1993). We find no error.