This is the first time you see Gladys, the artwork Phoebe made of a woman coming out of a painting; however this Gladys is different from the one in later episodes. The later Gladys had a red shirt, more hair, and two hands.
In the scene when Joey is asking Ross to show him the presents he bought, Joey uncrosses his legs twice.
As the Building's superintendent, Mr. Treeger should have known the heat can be turned off by turning the knob underneath the radiator.
Phoebe's grandmother is going through the obituaries and calls out the name Esther Livingston. The close-up of the obituaries page shows she is pointing at the name Richard Lilley, and there is no Livingston on the page. In addition, all of the obituaries are clearly for people who lived in the Los Angeles area, and this program is based in New York.
There is no Gershwin musical that has a 24 letter long title.
When Phoebe picks up Chandler and Joey in her grandmother's cab, you can see a cable attached to the rear of the car dragging on the curb.
Phoebe tells her friends that her dad ran out on her mother before she and Ursula were born. In a much later episode, when Phoebe meets her father, it becomes clear that he stayed at least so long as to sing lullabies to his daughters.
Joey turns the heating off by turning the knob underneath the radiator, but earlier on when he and Chandler meet two girls who can't fix their heating he says he doesn't know how to fix it.