Kevin: Can I bring my cat to work? He has terrible anxiety problems.
Abby Yates: Oh, I'd love to let you bring your cat to work, but I have a terrible cat allergy.
Kevin: I don't have a cat. He's a dog. His name is My Cat.
Abby Yates: You named your dog My Cat?
Kevin: Mike Hat.
Erin Gilbert: First name Mike, last name Hat?
Kevin: Well, his full name is Michael Hat.
After the meeting with the ghost of the mansion Erin hugs Abby and she gets the ectoplasm from her, but in the next shot it disappears.
The "Demonic Balloons" that attack the Ghostbusters are almost direct re-creations of real Macy's Thanksgiving Day Parade balloons from the 1930's. The filmmakers decided to use the real designs in order to represent the "spirits" of New York's history... and also because they were quite eerie and unsettling.