LONDON — It’s really not funny, but Phoebe Waller-Bridge can’t help it. She is re-enacting this YouTube video of a psychopath sitting dead-eyed in her prison uniform and recounting how she killed a man. When Ms. Waller-Bridge gets to the details — the woman drove a nail through her victim’s skull, strangled him and chopped his body to bits — she laughs, and then she sighs: “Terrible!”

Ms. Waller-Bridge, a writer and star of strange and beguiling comedic works, is tucked into a red leather booth in the lobby bar of the Soho Theater, eating a browning banana and searching for little openings to laugh about just about anything. She describes something she once did as “hilarious,” and then laughs at herself for thinking she is so funny. She tells me that she loves staring into the eyeballs of a live audience, but that on TV it’s like she’s acting for just one big shiny eyeball, and then she laughs because she’s suddenly become hyper-aware of my eyeballs.

She talks like a one-woman band, always pulling some strange new sound effect out of her body. She is 33 years old and just under 6 feet tall, and when she is paired on screen with men, she must deflate herself — “PFFFST”— to let them seem big. When she laughs, her voice opens into an off-kilter melody, as if her throat has recently taken up the xylophone. If you ever have the opportunity to make her laugh — it’s not hard — it will feel like she’s thrown her head back and released a song just for you.

Her one-woman play, “Fleabag,” hit the Edinburgh Festival Fringe with such force in 2013 that it left a smoldering Phoebe-shaped crater in the comedy landscape. Almost instantly, she was enlisted to adapt “Fleabag” for TV, create and star in another sitcom, write a weirdly funny murder show, and ultimately ascend to the “Star Wars” universe, playing a mouthy droid programmed to deliver “Solo” some comic relief.