Continuity mistake: When Greg sees Jack in the mirror, Jack has one hand behind his back and yet when Greg looks at Jack directly in front of him, both of Jack's hands are behind his back. (01:25:30)
Continuity mistake: In the scene where Greg comes in to his parents bedroom and they are having fun with whipped cream, there are 2 pillar candles by the door. These candles are seen in several of the shots showing Greg. The flames keep going out and relighting, but the candles are too new for the flame to be just dipping out of sight, and besides those sort of candles will often glow near the top when that happens. They must have kept blowing out between takes and the crew kept lighting them. (00:48:40)
Continuity mistake: During the fondue dinner, Little Jack is in his crib, which is right next to the table between Dina and Jack. Then in the next couple of shots the crib is gone, it then reappears again at various times with and without LJ. (00:38:30)
Continuity mistake: In the scene where the two sets of parents meet for the first time on the island, Bernie hugs Greg leaving his sweat mark on Greg's shirt which also looks wrinkled. This changes to there being no wetness at all, some wetness and then very wet again in between shots of him. When he enters the house, his t-shirt is totally smooth and dry. (00:21:25 - 00:23:20)
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.