Andrew Robertson's eyes were wide and blazing, as Mohamed Salah tried to lead him away. He had the kind of look you might expect someone who had just been mugged to sport — the shock, disbelief — as realisation kicked in.
'He's just f***ing elbowed me!' Robertson barked to Salah. His anger would have been plausible had he been cracked on the chin by an opposing player, but by an assistant referee?
Just when you think you have seen it all before in football, along comes something to leave you dumbfounded.
Constantine Hatzidakis had indeed elbowed Robertson, as Liverpool and Arsenal's players headed off at half-time.