They were shooting a crucial scene in director Howard Hawks' 1944 wartime drama "To Have and Have Not," but her head was shaking, as was her hand and the cigarette she was holding. And trembling was not in the script.
In that moment "the look" was born — the one that would make the sultry-voiced actress a screen legend and redefine sexuality for generations to follow.
Bacall, the Hollywood icon who taught Bogart how to whistle in the film that launched her career and turned "Bogie and Bacall" into one of the movie world's most celebrated couples, died Tuesday in New York, where she had lived for several decades. She was 89.
Her death was confirmed by Robbert de Klerk, co-managing partner of the Humphrey Bogart Estate with her son, Stephen Bogart. The cause of death was not disclosed.
In a statement released on social media, the Bogart Estate expressed deep sorrow and "great gratitude for her amazing life." Her daughter, Leslie Bogart, said the family was not releasing any other details at this time.
Few Hollywood careers began as memorably as that of Bacall, who won two Tony Awards on Broadway over an acting career that spanned more than 60 years.
She was a fledgling New York stage actress and a model whose pictures in Harper's Bazaar came to the attention of Hawks, who placed her under personal contract and cast her opposite Bogart, who at 44 was more than twice her age when they met on screen.
"Anybody got a match?" Bacall, appearing in the open doorway of charter boat captain Bogart's Martinique hotel room, asks in the famous scene. He tosses a small box of matches to the tall, slim young stranger in a tailored suit with padded shoulders. She takes out a match, strikes it and gazes indifferently at Bogart before lighting her cigarette.
"Thanks," she says, tossing the matchbox to him and leaving.
But as much a Bacall trademark as the look she gave him was her voice, kept at a low register at Hawks' direction throughout the film. It gave the young actress a seductive worldliness that was never so evident as when she delivered one of the most famous lines in movie history to Bogart.
"You know you don't have to act with me, Steve," she says to him. "You don't have to say anything and you don't have to do anything — not a thing. Oh, maybe just whistle.
"You know how to whistle, don't you, Steve? You just put your lips together and blow."
Hawks later said he told Bogart that he considered him "the most insolent man on the screen, and I'm going to try to make the girl just as insolent as you."
Warner Bros. trumpeted its "provocative" new discovery in the movie's trailer as "The only kind of woman for his kind of man!"
Critic James Agee wrote at the time that Bacall was "the toughest girl a piously regenerate Hollywood has dreamed of in a long, long while."
The on-screen chemistry between the two co-stars was an extension of what was happening off-screen. During the film's production, Bacall and the twice-divorced, unhappily married Bogart began an affair.
They were married in 1945 and teamed up in three more Warner Bros. movies over the next few years: "The Big Sleep," "Dark Passage" and "Key Largo."
"To Have and Have Not" showcased Bacall in "a perfect role that set her persona for life," said Jeanine Basinger, author of "A Woman's View: How Hollywood Spoke to Women" and the head of the film studies program at Wesleyan University.
"So she was a legend from the very first minute," Basinger told The Times in 2004. "And she was so unique — her looks, her style, her voice."
In the years after their marriage, Bacall starred in films such as "Young Man with a Horn" with Kirk Douglas, "Bright Leaf" with Gary Cooper, "How to Marry a Millionaire" with Betty Grable and Marilyn Monroe, "Blood Alley" with John Wayne, "Written on the Wind" with Rock Hudson and "Designing Woman" with Gregory Peck.
But Bacall put her marriage before her career.