The first-half of Liverpool's clash with West Brom in the Premier League had fans talking about the 'Operation Anfield Exercise' announcement.
Some supporters were left baffled by the call that commenced the mysterious exercise before later giving the all clear.
The announcement could also be heard by viewers watching the action on Sky Sports.
A number of amusing and inventive reasons behind the announcement were shared but the real reason can be revealed - and it's nothing that fans need to pay much attention too.
'Operation Anfield Exercise' is an exercise for the stewards, who must be ready to deal with an emergency at a moment's notice, and the announcement acts as an instruction for stewards to get into their correct positions inside the stadium.
At the same time, the turnstiles around the ground are tested to ensure they are functioning properly in case a mass exodus from the stadium is required, making sure supporters can leave quickly but safely.
The announcement is made a number of times a season in order to test that everything is working accordingly and that, should the worst happen, the stewards in the stadium can deal with any issues that arise.
