Other mistake: The Monster appearing in the pilot and causing the turbine to explode is a mistake (not trivia). This is actually an artefact of poor CGI effects that was left in the show in error. It was confirmed by the producers. You can see it best here: http://www.lostpedia.com/wiki/Image:Turbine_Explosion.gif.
Flashes Before Your Eyes - S3-E8
Other mistake: In the series 3 episode "Flashes Before Your Eyes", several scenes purport to take place in England. However, the poster for the Royal Scots Guards which Desmond looks at as he passes the Army recruitment office has the American spelling for "honour".
Homecoming - S1-E15
Other mistake: Ethan kills one of the survivors. Sawyer thinks it's Steve but Hurley corrects him and tells him that it was actually Scott. They make a point of Scott being the deceased and Steve being the one people mix him up with. According to the actors playing Scott and Steve it was in fact Steve who got killed but the producers messed it up.
Other mistake: When the doctor stops Sun on the streets to tell her that Jin is the one who can not have children, at one point the subtitles say "You're husband." The correct spelling would be "Your".
Other mistake: When Jack and Rose talk the second time on the beach, they talk while it is cloudy and overcast. However, as Jack stands up to leave, he is brightly illuminated by sunshine.
Other mistake: In the scene with Sawyer and Michael drifting on the pontoon, where Michael is crying, you briefly see a boat with a mast in the background in one shot over Sawyer's right shoulder as he faces the screen, just before he says "Are you allright Mike?". (00:38:10)
House of the Rising Sun - S1-E6
Other mistake: When Walt says to his dad that his mum never talks about him, something briefly blows into shot at the top of the screen. There is no logical explanation for this as they are walking by the water, under no cover and nothing is around. (00:18:50)
Answer: Using a mold, a realistic pregnancy belly is made of latex (rubber), including the distinct belly button, to suit the proportions of Emilie de Ravin who plays Claire. It is then painted with a special paint/adhesive compound that adheres to the surface and for shots of the actual belly, additional veining and stretch marks are airbrushed on.
Super Grover ★