Ella Purnell stars as Rhiannon Lewis in the new six-part Starz drama Sweetpea, about a young woman who transforms from meek wallflower to emboldened serial killer. Think Dexter meets female rage.

Purnell, who can also be seen in hit shows Yellowjackets and Fallout, says taking on this role in particular scared her because of its moral ambiguity.

“That was our goal with this series, was to conflict the audience, you know, make them relate to Rhiannon’s emotions and her motivations, but obviously not her actions,” she tells ABC Audio. “And that was just really interesting to me. I didn’t know if I could do it, and it really scared me.”

She was able to tap into Rhiannon’s rage — which manifests into some pretty intense kill scenes — by shaking off any inhibitions she may have had while filming.

“[I had to] not think about the cameras, not think about all my mates who are standing around on the set and just like let it out,” she says. “And it actually became quite therapeutic. And I think with all of those scenes, I didn’t practice them, I didn’t plan them, I didn’t really know what was going to come out and that was quite exciting.”

So what’s one pet peeve that would land someone on Purnell’s metaphorical “kill list”?

“One big one for me is … when people like constantly interrupt you,” she says. “We all have that one person who every time we speak, they decide to pipe up. And it’s only when we speak and they cut you off.” 

Sweetpea debuted Thursday on Starz and will air new episodes every Friday.

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