In the film, a shark is roaming around in the ocean, thus frightening a small worm. As he sees the shark come closer, the worm goes into a panic; however, as the shark is about to eat him, he instead greets the scared worm and introduces himself as Lenny. This makes the worm faint and, worried that he had scared him, Lenny apologizes and tries to wake him up. As he struggles to rescue him, Lenny's brother Frankie calls for him and tells him to hurry since their father is waiting for them. Lenny turns his attention back to the worm and manages to save his life, and he slides up the hook, unharmed. Lenny encounters the approaching Frankie and tells him he almost gave him a heart attack since he startled him. When Frankie asks Lenny what was he doing, Lenny thinks up a lie and, as he brings out some flowers, tells him he was picking them for him. However, Frankie hits them out of Lenny's fins and he tells him their mother told them it's not okay to hit. In response, Frankie rolls his eyes and punches Lenny in the shoulder, telling him, "Mom's not here." Then he and his brother swim back home, with Frankie humming the Jaws theme song to tease Lenny, who tells Frankie not to sing it as he doesn't like it (which Frankie is confused by since it is their theme song).
Later on, Lenny and Frankie arrive at Lino's office and Frankie apologizes to him for being late and says the reason is because Lenny had an accident, which he jokes that Lenny being born was his accident. Feeling hurt by this joke, Lenny does a sarcastic laugh and tells his brother that he's a "comic genius". When Sykes tells Lino that Lenny isn't a killer, the gangster insists his son is a coldblooded killer and tells Sykes to look at him; but when they do, Lenny is seen swiveling in his chair, which irritates Frankie as he is tired of his brother's kind behavior. Infuriated, Lino fires Sykes and orders him to start paying him after hitting him into the wall as Lenny and Frankie watch the porcupinefish go flying.
Unlike the others, Lenny is a very happy and friendly shark who is willing to help anyone out and keep secrets. He is a vegetarian and because of this, he was afraid of admitting this to his father.
- Lenny is sometimes thought to be the tritagonist of the film. This is not true as he had a bigger role than Angie.