At Roddenberry's insistence, Spock was the only character retained for the second pilot, "Where No Man Has Gone Before". However, NBC demanded that he be only a background character, and when it went to series, the tips of Spock's ears were airbrushed out on promotional materials. It was during early episodes such as "The Corbomite Maneuver" and "The Naked Time" that Nimoy came to understand the nature of the character. After eight episodes, NBC executives complained to Roddenberry that there was not enough Spock in the series; "Spockmania" had begun. In response, Spock was moved to a more prominent role within the series, such as taking the lead role in "This Side of Paradise" over Sulu. The popularity of the character caused frictions with Shatner, and rumours spread that he was going to be dropped from the show and replaced as the lead by Nimoy as Spock. A drawn out contract renegotiation at the start of resulted in Roddenberry considering whether or not to replace Nimoy and the character. Both Mark Lenard and Lawrence Montaigne were seriously considered.