When Rhonda is explaining to Joey the difference between the white blazers and the blue blazers, someone wearing a white blazer appears and disappears between shots.
A teacher or a parent would be accompanying the children while Joey escorts them throughout the museum.
Ross clicks the timer and tells Monica and Rachel their 30 seconds is up, but the timer is showing 5 mins 23 seconds on the display.
When Ross invites Joey to sit with him in the cafeteria, a movie light is visible behind Ross's head in the reflection in the cafeteria door window.
In future episodes it is revealed that Chandler is afraid of dogs, yet when he enters Monica's apartment while Phoebe is singing to the puppy, he shows no emotion and even cracks a joke about it.
As a full grown adult and one of Ross's best friends, Joey should know Ross's nickname is not Dr. It's his academic and professional title.