Lauren Bacall for "To Have and Have Not" (1944), Bacall was so nervous that, to minimize her quivering, she pressed her chin against her chest, faced the camera, and tilted her eyes upward. This effect, which came to be known as "The Look", became another Bacall trademark, along with her sultry voice. Bacall's character in the film used Slim Hawks' nickname "Slim", and Bogart used Howard Hawks' nickname "Steve". The on-set chemistry between the two was immediate according to Bacall. She and Bogart (who was married at the time to Mayo Methot) began a romantic relationship several weeks into shooting. Bacall's role
What Love Is Made Of extremely positive about "What Love Is Made Of", describing it as "darker than anything" from "On a Mission", while calling it "slinky". The reviewer went on to commend the "irresistibly pouty" chorus. Pitchfork Media's Katherine St. Asaph commented that, in the song, the singer "sound[ed] completely enthralled, by either her lover or the music" and complimented her voice, noting that it seemed "ten times bigger than before". Jordan Sargent of "Spin" magazine called the track "exuberant" and highlighted Katy's vocal performance, which he deemed "typically fantastic", while the team from pop music website Popjustice gave "What Love Is Made Of"