Visible crew/equipment: In the scene where Greg is leaving a message on his parents answer machine about going to their house in the Byrnes' motor home, you can see that it is just Stiller standing in front of a blue screen, obviously they wanted to add the scene in after shooting had finished. (00:11:55)
Visible crew/equipment: As they start out on the trip, when they are showing Jack & Greg up front, you can see in the window right behind Greg a reflection of two crew members wearing sunglasses. They stay in frame for about 5 seconds. (00:13:21 - 00:13:26)
Visible crew/equipment: After Jack says, "Only the captain gets to make announcements, Greg," in the next shot of Greg the boom mic and pole are nicely visible over Jack's reflection in the window, to Greg's right. There are two other shots of Greg at this angle - one previous and one following, but unfortunately the equipment is not seen. (00:13:25)
Visible crew/equipment: While passing the frat-house bus, in the close-up, as the two girls are about to flash, the reflections of the camera and two crew members moving on the crew's vehicle are visible on the glass window. (00:14:15)
Visible crew/equipment: When Pam and Greg walk to the RV and open its door, in the next shot just as Moses chases Jinxy, behind Jack, Roz and Dina, the reflection of a hunched over crew member, wearing a red shirt, is visible. Don't confuse his reflection with Bernie's, who is also wearing red. (00:36:10)
Visible crew/equipment: When Officer LeFlore arrests Bernie and Greg, lovely reflections of the reflector screen are seen in the lenses of the officer's sunglasses. There are other moments in the film where the reflector screen is visible in lenses. (00:51:40)
Visible crew/equipment: When they are playing football, they show a close up of Jack's face after Dina makes a touchdown and she and Bernie celebrate. In the close up of Jack's face and sunglasses, in his left eye, you can see the reflection of a square camera light. This shows up again right as Jack is about to be tackled by Bernie, this time in his right eye. It follows Jack as he rises in the air to catch the ball. (00:52:15 - 00:54:45)
Visible crew/equipment: When Jack and LJ take off in the motorhome, while ignoring everyone's shouts to come back, the crew's blue tent is visible in the reflection on the motorhome's large side, as it turns the corner. (01:35:35)
Visible crew/equipment: Two shots after Gaylord touches the boob, you can see a boom mike dip into view.
Visible crew/equipment: When Jack drives away from the Fockers' house the filming crew's white pop-up tent is reflected on the RV.
Answer: Truth serum doesn't automatically make you speak the absolute truth - all it can do is make you say what you believe to be the truth. If Gaylord believed himself to be Jorge's father, then he would say that under the truth serum, even if it ultimately turned out not to be the case.
Tailkinker ★
Gaylord (Greg) was also drunk when he went on his monologue of spilling "secrets" about others in the room.