Earlier in the episode Monica seems to be under the impression that Chandler is allergic to dogs. However, in The One with Rachel's Book (2000) Monica corrects Chandler's vision of their future by stating that they will have a dog instead of a cat, which he agrees to.
After Monica and Phoebe sneak Clunkers back into the apartment, Ross distracts Chandler by telling him Monica is upset because as a child, their father also disliked dogs and Monica had to give up her dog 'Rover' and Chandler believes him. However, Monica and Ross actually did have a family pet dog Chi Chi that has been mentioned a number of times since season one.
In this episode Chandler is afraid of dogs, but in The One with Joey's Porsche (1999) he agrees to take care of three puppies.
In order to determine all 50 states, Ross suggests that anyone who ever saw a map or a globe should know all 50. Globes don't show states. They show countries.
When looking out of Ross's window, the building that Monica and Chandler live in is shown and you can see that none of the windows on the building have a balcony. When talking on the phone to Phoebe, Monica is looking up indicating their apartments are not level- this could mean Monica's apartment is on a floor that is not shown and could have a balcony except she can "see" her couch and the dog so their apartments would have to be level.
It appears that Ross doesn't like ice cream, but in The One Where Ross Dates a Student (2000) you can see him and Elizabeth both eating ice cream whilst on their date.
On a couple of occasions, the cast including Chandler refer to the dog as as a female, but at one point, Chandler says, "I couldn't find him."
When Ross is trying to list all the states, Joey believes Ross made the name "Utah" up. Joey is a Knicks fan, and Utah has an NBA team, so that simply can't be.