Revealing mistake: As Ed slowly backs away from the camera (from the foreground to the background), the towering Scrapper robot moves slowly forward (from the background to the foreground) to take Ed's place facing the camera. The lumbering robot is plainly casting a long shadow across this night-time shot towards the right side of the screen. But, as Ed and the giant robot pass one another, the CGI robot's shadow never falls across Ed at all. Throughout the shot, Ed remains uniformly illuminated, revealing that the digital-effects artist neglected to add the shadow passing over Ed. (00:38:55 - 00:39:19)
Revealing mistake: While Matt is lying in his hospital bed, he hangs up on a call with Emma. You can see his left foot moving. He's not supposed to be able to feel or move his lower body.
Revealing mistake: There are bullets placed on the counter, the one casing has a hole in it from being drilled to show it's a dummy round and there's no gunpowder in it. (00:14:45 - 00:15:20)
Revealing mistake: The bullets the priest takes out of the ammunition tray have no primers. (01:01:33)
In Sickness and in Health - S4-E18
Revealing mistake: The baby is obviously a mannequin or doll when it's underwater.