My cat was up all night throwing up. So obviously I was up all night holding her hair.

The joke hinges on anthropomorphism and a familiar caregiving cliché. “Holding her hair” is a stock image of helping a drunk or sick friend vomit; applying it to a cat (which has no long hair to hold back in the human sense, and no social expectation of such care) creates an absurd mismatch. Silverman uses the deadpan “So obviously” to heighten the comic logic, implying an over-the-top, intimate caretaking response to a mundane pet problem. The line also lightly satirizes how people project human rituals onto pets, turning private inconvenience into a performative act of devotion.