a logical place to bring back the bees that were used in the season premiere, "Herrenvolk", feeling it was important to not have something paranormal happen to Skinner in this episode considering that had been done in the previous season. Live bees were used for filming, but showed up poorly in the footage; visual effects technician Laurie Kallsen-George then spent nine days digitally enhancing the footage to improve upon this. The virus-carrying bees would later form a central plot point in the series' 1998 feature film adaptation. Director Kim Manners noted that the episode "was a really good show for me, because I had not got a chance to work with Mitch. And they wrote a great script, you know? It was really something he could sink his teeth into and he just did a great job. Bill Davis was fabulous in that show too". This was the second episode of the series to not feature Scully, the first being the second season episode "3". Guest actor Morris Panych, portraying the Syndicate assassin The Grey-Haired Man, makes his last appearance in the series in this episode. Panych had previously appeared in "Piper Maru", "Avatar", "Herrenvolk" and "Memento Mori". Broadcast and reception "Zero Sum" premiered on the Fox network on , and was first broadcast in the United Kingdom on BBC Two on . The episode earned a Nielsen household rating of 11.7 with a 17 share, meaning that roughly of all television-equipped households, and of households watching television, were tuned in to the episode. A total of viewers watched this episode during its original airing. The episode has received mixed to positive responses from critics. Zack Handlen, writing for The A.V. Club, rated the episode an A, calling it "utterly bad-ass". Handlen felt that the episode effectively toyed with the series' usual narrative structure, making lead character Fox Mulder seem "nearly as much of an antagonist" as The Smoking Man; Handlen also felt that "Zero Sum" gave significant insight into the character of Walter Skinner. Paula Vitaris, writing for Cinefantastique, rated "Zero Sum" one-and-a-half stars out of four, noting that its "pacing and tone are off". Vitaris felt that "Duchovny and Pileggi give good performances", despite Pileggi seeming "unintentionally comic" at times; though she noted that "an episode without Scully feels pretty empty". Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files,