When Gunther is asking Rachel for her birthday, Ross starts to say his birthday is in December. It is later revealed that his birthday is in fact October 18th.
Gunther asks Rachel what her birthday is, as she replies that her birthday is May 5th. However, in The One with Chandler's Dad (2001), a policeman notes Rachel's an Aquarius, which would put her birthday between January 21st and February 19th, and not in May.
In the pub scene, when camera is on Chandler, Kathy is rubbing Joey's back with her right hand and very next second when camera is on Joey and Kathy, Kathy's hand is in front and beneath the table. And again when Chandler is facing the camera, Kathy is rubbing Joey's back and very next second in the long shot when all the three are in frame Joey and Kathy are holding hands. In the very next frame when the camera is on Chandler and he leaves the table, Kathy's hand is on Joey's back.
Phoebe picks up the same napkin twice.
While Chandler is chasing Kathy, he runs into a bunch of leashes with dogs at the end. You can hear the dogs barking, but the dogs are visually just walking around.
When Phoebe shows the shoes she makes by placing her foot on the coffee table, the mike is visible at the centre of the top of the screen