Carol's hair-pin changes position (from being at the level of her ears to the level of her neck and backwards) when she's making her night visit to Melvin
When Simon picks up his dog from Melvin after returning from the hospital: he's at Melvin's apartment door in a wheelchair but from previous scenes we know there are stairs between the apartments.
Verdell is played by six different dogs. All of the dogs are the same breed; Griffon Bruxellois or Brussels Griffon. More information can be found about these dogs here.
Q
What is that song Vincent plays in Simon's studio?
A
A cover by The Spin Doctors of the Jimi Hendrix song "Spanish Castle Magic."
Q
What is the song Melvin plays in his car marked 'To Use As Icebreaker'?
A
It's called "Days Like This" by Van Morrison. The rest of the songs and their corresponding scenes can be found here.