Her favourite snack, perhaps?!
Ditching the traditional scary dress code for something a little more unusual, Katy definitely turned heads in her hard-to-miss orange ensemble.
A solid effort, don't cha think?
Donning her giant Cheeto costume, Katy was covered from head-to-toe with just her face on show as she made her way into How To Lose A Guy In 10 Days star Kate Hudson's Hollywood Halloween bash.
In case other party-goers didn't quite catch on to Katy's outfit choice, the 'Dark Horse' singer clutched onto a bag cleverly made out of a Cheetos crisp packet.
You know, just to highlight the resemblance...
Joining Katy at the star-studded party were a whole host of famous faces, including the likes of Jessica Alba, Courteney Cox and fiancé Johnny McDaid, Grown Ups star Adam Sandler, Glee's Diana Agron and, of course, the host herself, Kate.
Channeling their inner rock Gods, Jessica chose to dress up as Guns 'N' Roses frontman Slash, while Kate and her pals decided to do their own take on popular TV series Sons of Anarchy in their biker gear.
Sharing a group shot from the bash, Kate said: "Mother of Anarchy is taking her daughters to a little party.... #HappyHalloween #hudsons #partytime."
Meanwhile, Friends star Courteney Cox made sure to give other guests a fright in her spooky ensemble.
As Johnny transformed into Dracula, Courteney gave her best creepy doll impression, painting herself white and donning a plaited blonde wig.
Along with a photo of herself and her fiancé in their Halloween getup, Courteney tweeted: "All dolled up and ready to go out."
Oh, Courteney you joker, you!
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Check out other celebrity Halloween costumes from over the years in the gallery below: