United Kingdom, June 7 -- Harrison Ford agreed to join the cast of Shrinking after admiring Jason Segel's private parts.

The Indian Jones star, 82, had never heard of Jason when he was asked to join the hit Apple show, and watched him in Forgetting Sarah Marshall before getting involved -which famously features two scenes of Jason going fully-frontal naked.

Jason has now opened up about Harrison's decision to sign on to Shrinking after they sent him two of Jason's films to consider - The End of the Tour and Forgetting Sarah Marshall.

The actor, 45, told Variety in an interview: "He didn't know anything about me. They sent him The End of the Tour and Forgetting Sarah Marshall.

"Then, apparently, (Shrinking producer) Bill Lawrence got a...