Sara and Scott chose to be security guards on the challenge and believed that they were in charge of checking that the housemates were staying still inside the BB Museum.
However, when the duo were in the Diary Room, Big Brother told the other housemates that they didn't really have to play living exhibits for the whole challenge.
They were informed that they only had to stand still and not talk for the first hour. The real task is for them to convince the security guards that they have been still and not talking throughout the day.
In reality, the other housemates - Adam Kelly, Luke Scrase, Ashleigh Hughes, Luke Anderson and Deana Uppal - have been sneaked off to a pyramid and secret chamber, which is filled with treats. The housemates must crawl through the pyramid and take off their outfits to get in the chamber.
When a red light flashes, they are alerted to the security guards heading back into the museum and must return before they are discovered out of place and out of costume.
Each trip into the secret chamber will earn them more treats.
Scott, Ashleigh, Deana and Adam are the four housemates facing possible eviction this week.
Big Brother continues daily on Channel 5. The show concludes on Monday, August 13.