Caroline Wozniacki serving for the match when Alizé Cornet's 'phone rings (screenshot from YouTube video)
We've all heard those announcements at the theatre, the cinema, a classical music concert, a live sporting event or whatever.
The reminder to those present to (if the organisers are feeling particularly polite) "Please turn off you mobile 'phones". Or at least put the ruddy thing on mute.
No sooner said than done. And woe betide you should you fail to do so.
But what happens when it's not a member of the public but one of those being watched or listened to, who forgets?
It was a first round match at the Swedish Open in Bastad between the world's number one ranked woman player, Caroline Wozniacki from Denmark and France's Alizé Cornet.
At 6-4, 5-3 and 40:30 up, Wozniacki was serving for the match when she - and everybody else present - heard a 'phone ring.
Wozniacki kept her cool and prepared to serve again, but once more the wretched thing went off.
Bemusement from Wozniacki and then a huge smile and laughter from everyone as the camera focused on her opponent who, realising she was in fact the offender, hurried to her kitbag to turn the thing off.
Applause and more laughter all round although it was hardly the "tremendous stuff" as suggested by the commentator on the accompanying video.
Wozniacki lost the game but went on to win the match 6-4, 6-4.