The director's dog, Garrison, was cast as the protagonist's pet, but he was a terrible performer. He went into a starry-eyed coma anytime the cameras turned on and they were only able to get any activity out of him by heavy bribery with treats.
A few months into post-production, the director's neighbor shot himself in the apartment below hers. He was DOA; the building was taped off by police, and the night played out very similarly to the scene in the film.
See "In Memory of David" in the closing credits.