Jennifer Tilly does not intentionally use a "fake" voice in every movie role; rather, her distinctive voice is part of her natural speaking style.
Tilly's breathy, high-pitched vocal tone has become a signature trait that complements the unique and often eccentric characters she portrays. Over time, she has embraced her voice as part of her on-screen identity, using it to enhance the comedic, mysterious, or playful elements of her performances.
In interviews, Tilly has acknowledged that her voice stands out and has contributed to her being cast in certain roles, such as Tiffany in Bride of Chucky and Celia in Monsters, Inc..
This voice has sometimes been exaggerated for comedic or dramatic effect, depending on the role, but it remains an authentic part of her persona