The movie borrows many elements from Émile Zola's novel Thérèse Raquin. Tae-ju is named after Thérèse and Lady Ra is named after Madame Raquin.
The original Korean title directly translates to "Bat".
The first mainstream Korean film to feature full-frontal male nudity.
There is a seemingly random brief shot at around 1:20:25 of a blood red ceiling with a single lightbulb. It's an intentional homage to one of William J. Eggleston's most famous photographs, entitled The Red Ceiling.
The 148 minute Director's Cut of the film is Park Chan-wook's preferred version of the film. To date, it has only been released in South Korea and France on DVD and Blu-ray. All other home video releases (including the US Blu-ray and DVD) only contain the theatrical cut.