BBC's Line of Duty returned on Sunday night for season six - and fans were left questioning what the term CHIS meant on the crime drama.
Fans of Jed Mercurio's action-packed series were excited to see plenty of drama on their screens as AC-12 officers Superintendent Ted Hastings, DI Kate Fleming and DS Steve Arnott try to bring down corrupt officers in the police force.
But there was one thing playing on viewers' minds as they tuned in to watch the first episode of series six on Sunday.
Lots of people took to Twitter to ask the same question, as they were eager to find out what the acronym CHIS stands for, as it is used very often throughout the programme.
Taking to Twitter mid-way through the episode, one person wrote: "Be honest. You googled CHIS in the middle."
Another wrote: "So, I guess Series 6 of #LineofDuty means we're all ready to collectively ask... What on earth is a chis?"
Viewers will be happy to know that CHIS stands for Covert Human Intelligence Source - meaning a person who establishes or maintains a personal or other relationship with another person for the covert purpose.
Those who managed to find out what the term meant shared the information on social media.
A third penned: "Spent the whole of #LineofDuty wondering what a CHIS was so was glad when the announcer gave it during the end credits (Covert Human Intelligence Source). Brilliant story as usual."
In Sunday's epic comeback episode, fans were excited to see Kelly Macdonald take on the role of DCI Joanne Davidson in the BBC series.
Kelly joined the cast as the latest boss leading an important case, an unsolved murder, with Detective Inspector Kate Fleming on her team.
Some viewers immediately suspected the newcomer was hiding something, due to her suspicious behaviour.
But some viewers were pretty distracted from the chaotic scenes, and it was all thanks to DCI Davidson's voice.
The actress' familiar vocals were featured in Disney Pixar hit Brave, with Kelly voicing Princess Merida.
Some viewers tuning in to the BBC series couldn't help but hear Merida every time DCI Davidson spoke on the show.
Viewers took to Twitter to confess they were struggling to unhear the Disney character, every time Joanne shouted orders on the BBC show.
One fan said: "When I hear Kelly Macdonald I just hear her as Merida from Brave."
Another agreed: "I can’t hear Kelly MacDonald without seeing Merida."
A third added: "Merida has become a cop!"
*Line of Duty continues Sunday at 9pm on BBC One.
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