I Have a Tiger (1979)

A little boy has a tiger as a pet, but it's a secret. The widemouth of the apartment building is Miss Kotilainen, who is always complaining about everything. Other people in the building have their own secrets too. After a lot of those secrets are uncovered, a party is held that melts the heart of Miss Kotilainen. After that, Kalle the Tiger won't have to be hidden no more.