What Could Have Been: There was supposed to be a scene after Ace crashed his car while chasing Dan Marino's kidnappers. The white pigeon landed on his car, he got it singing "I got the white pi-geon! I got the white pi-geon". Then, in a parody of The Birds, he is surrounded by birds that started tearing him apart. Then he wakes up with a big "whew." It was removed from the finished film since it was too dark, but ironically in the commentary Word of God says it was funny on paper.
The original concept is the Pet Detective character was a bumbling idiot, until Jim Carrey was cast and his character was rewritten.
According to IMDB, Rick Moranis was considered for the role of Ace Ventura!
Originally Ace wasn't written to be animal-related, but more of a generic Sherlock Holmes parody. Screenwriter Jack Bernstein came up with the pet detective idea after watching a David Letterman sketch about pet owners.