
As they travel by zeppelin, William tries to encourage Walter that he no longer needs Bell's guidance. Peter realizes that when Olivia is scared, she retreats to somewhere safe, and suggests they search her mind's version of Jacksonville, her childhood home. The three are unable to find clues to Olivia's ego, something that William thought would be present if Olivia was looking to be found. After evading a crowd and a trap set by a false vision of Nina Sharp ( Blair Brown), they arrive at Bell's office, where they find William waiting for them as an animated cartoon. Walter sees someone sending a Morse code signal from William Bell's office in one of the World Trade Center buildings. Inside Olivia's mind, Walter and Peter find they stand out as invaders, and the people that populate her mind, including a vision of her step-father (Chris Bradford), seek to stop them. Walter comes up with a plan: he and Peter ( Joshua Jackson) will enter Olivia's mind with the aid of LSD to locate her ego and help it to regain dominance in her mind, while Walter hopes to download William's mind into a computer. They realize that Olivia is unaware that she has been possessed by William's mind, and instead has likely locked her ego away, making it difficult to contact her by normal means. Walter ( John Noble) and William believe that they have less than a day before Olivia's mind will be lost. The mind of William Bell ( Leonard Nimoy) still possesses Olivia's ( Anna Torv) body after several failed attempts to extract it to recently deceased corpses. Critical reception was generally positive, as multiple reviewers praised the creativity of the writers. An estimated 3.6 million viewers tuned in, helping the episode earn a 1.4 ratings share for those 18–49, tying a series low. The episode first aired on Apin the United States on the Fox network.

Production of the animated portions was completed by Zoic Studios in an eight-week effort, the largest amount of work hours required to produce a Fringe episode. It marked the return of previous guest actor Leonard Nimoy, who had announced his retirement the previous year. Wyman and Jeff Pinkner, while Wyman and Pinkner co-wrote the story with Akiva Goldsman. The episode's teleplay was co-written by J. The narrative followed the Fringe team's attempts to extract William Bell from Olivia's brain by entering her mind with the help of LSD. " Lysergic Acid Diethylamide" is the 19th episode of the third season of the American science fiction drama television series Fringe, and the 62nd episode overall.
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Peter (left) and Walter marvel at the animated world inside Olivia's mind while talking to William Bell (right)
