A woman's right to shoes (a.k.a. no shoes, no service) - S6-E9
Revealing mistake: When Charlotte and Carrie walk down the street there's a group of bystanders behind watching the filming. One of them is even taking pictures.
Revealing mistake: When Sam and Jerry watch the billboard, a blue car passes by and the driver slows down and stares at the filming.
Lights, camera, relationship - S6-E5
Revealing mistake: Right when the episode starts, a group of bystanders gather to stare at the filming.
Revealing mistake: While Carrie and Sam are in the bar car, the train bumps and the passengers swerve to the left.Problem is, they do not move in sync, revealing the camera trick. The first one to move is the girl in front, and a second later the woman on the left moves.
Revealing mistake: When the baby is about to be baptised, it is replaced by a blatant doll: The doll's arm is stretched out (as opposed to the real baby's arms, tucked in his robe), and the doll's hair is very obviously painted.
Anchors away - S5-E1
Revealing mistake: Exactly half a second after it starts to rain at the museum, the street is already soaking wet and covered in puddles.
Anchors away - S5-E1
Revealing mistake: When the cat is playing with the navel, it moves as if it has a life of its own, which is absurd and reveals that there was some wire or mechanism to move it.
Anchors away - S5-E1
Revealing mistake: When Miranda is breastfeeding the baby, there 2 obviously different breasts and bodies: In the close-up (real breasts) the areola is small; but the prosthetic breast has much bigger areolas.
Revealing mistake: When the episode starts and credits are still rolling, there are obvious groups of bystanders watching the filming and staring straight at the camera.
Revealing mistake: When breakfast arrives, Samantha mimics eating and chewing, but her fork is very obviously empty.
I heart ny - S4-E18
Revealing mistake: When Sam and Carrie walk, bystanders sneak-in shot to stare at filming.
Revealing mistake: When Charlotte brings dinner, the little boy can't help staring at the camera.
Revealing mistake: When Tray and Charlotte stand by Tyffany's door, bystanders on the right and on the left sneak-in to see the filming.
Revealing mistake: After Carrie leaves home because Aidan is fixing the floor, Charlotte and Trey walk down the street. There's a group of people on the left who can't stop looking at the camera.
Revealing mistake: When Trey and Charlotte stop in front of Tiffany's, all of the passers-by stare at the camera. There's even a bald man in a white T-shirt who stops dead in his tracks and sneaks his head in between Charlotte and Trey while staring.
Revealing mistake: When breakfast is served, Samantha mimics eating and chewing, but her fork is very obviously empty.
Hot child in the city - S3-E15
Revealing mistake: When Carrie is scooting through New York, there are literally crowds of people gathering together watching the filming and staring at Carrie and the camera. There's even a big group standing in the middle of the road despite the traffic with a cop in front controlling the situation.
Revealing mistake: When Sam is having sex with the doctor, you can tell she has a skin-coloured bra to stop her breasts from being shown.
Answer: A popular brand of sexual lubricant. See http://www.k-y.com/index.jsp.
J I Cohen