Patzer

At one point in the ping-pong game, Monica scores a point but Mike informs her she has to forfeit the point because her non-paddle holding hand touched the table and that is against official rules. Later in the game, Mike scores the game point and Monica gets upset that she lost. However, by his own logic, Mike could not have won because his non-paddle holding hand touched the table before he scored.

When Monica and Mike play ping pong, you can see there's nobody behind Monica. In the next shot though, when they fight whether the ball missed the table or not, you can see there's a woman sitting on the chair behind Monica. A moment later, the same woman walks in with another woman and sits at the checkers table.

When Monica hurts her hand playing ping pong she drops the paddle on the floor but when Chandler steps up to play for her he suddenly has the paddle in his hand. Correction: In between the shots where Monica hurts her hand and Chandler stepping up to play in her place, there is a lengthy shot of Mike and Phoebe talking, during which time, Chandler could have picked the paddle up from the floor.

When Chandler asks Ross' laptop to check his e-mail, he taps Ross chest with his right hand, but in the next shot he's using his left hand.

When Ross and Charlie are up against the wall hiding from the other scientists, they have full drinks. As the camera cuts between Ross and Charlie, you can clearly see that the drink glasses go from full, to almost 1/3 gone, to almost full again.

Early on in the show, the writers decided to dispatch Phoebe's love interest David "The Scientist Guy" to Minsk. Which was unfortunate because from there on, just about every reference they made to Minsk was incorrect. The city is in Belarus, not Russia, something David should have known. And the sanitation strikes he mentions could never happen: Belarus is a famously authoritarian, neo-communist society ("Europe's last dictatorship") where protest of any kind is not tolerated. Anyone organizing a strike would no doubt end up serving a long jail sentence.

When Joey comes to Rachel's room and knocks on the door, Rachel tells him to come on in and that the door is open. But they are staying at a hotel and there is no way to leave a hotel door unlocked.

When Joey's in the bedroom with Rachel he says he's as curious as George. Rachel seems to not know who he's talking about, but in one of the episodes with Ross's monkey she had a Curious George doll. Response: The Joey created phrase "curious as George" is not an obvious reference to the character "Curious George". When Ross says the phrase "Curious George, Rachel immediately knows what that is.

When Rachel bursts into Monica and Chandler's room and opens the curtains to reveal it's no longer raining, the scene shows a completely static beach, where the waves are not moving.

Ross loses everything off his hard drive when Chandler inadvertently activates an email virus, meaning Ross and Charlie have to re-create his keynote speech from memory. However when Ross is delivering that speech, he's using visual aids. Wouldn't the PowerPoint slides have also been deleted?

When Ross is talking to Jarvis at the bar and Jarvis' wife walks up; Jarvis says, "Oh you're back", and then stands up. As Jarvis stands the wall behind him begins to rotate counter clockwise.

When Ross is sitting and talking to Jarvis (the man who admired his speech), Jarvis's wife appears. Just as Jarvis is saying, "Oh, you're back," you can see the wall behind him start to move (probably in preparation for the next few camera angles).

When Ross catches Chandler, Monica, and Phoebe listening at the wall to the adjoining room. When the door is open, it's clearly a corridor with Chandler and Monica's room number on the outside.

There's also a toilet in the corridor.

When Mike and Monica are playing ping pong, after the first point is played Mike claims that if either player touches the table with their non racket bearing hand, he or she forfeits the point. However for the final point of the second game Mike clearly puts his hand on the table before hitting the game winning shot. By his rules Monica should be awarded the point. As astute as Monica is portrayed to be she would surely have picked up on this.

Ross hands out all-access passes to the conference to everybody yet when Joey and Rachel want to get into the conference to get food, they steal random passes off the welcome table.

At the hotel arcade, sound effect chimes from an electromechanical pinball machine can be heard, even though all three pinball machines in the room (Surf N' Safari, Fun House, and Diner) are all solid state machines, which would not make such sounds.

When Mike and Monica start playing ping pong, you can see the boom microphone moving out of the top of the screen.

During Ross' keynote speech, he refers to the then recently discovered dinosaur Giganotosaurus as a herbivore, suggesting he is not going to discuss the carnivores. Giganotosaurus is actually one of the largest known terrestrial carnivores of all time.

In the first scene at Central Perk, when Ross hands out the passes for the conference, Rachel is handed Joey's pass and Chandler is handed Phoebe's pass.