The notion that highly trained assassins would be exhibiting any overt signs of stress or fear before, during, or after doing their job is beyond me.
They would surely show a desire to leave the scene as quickly as possible though, right? As far as they know, Skirpal is already in trouble in his front garden with the police on their way. Why hang around? If they have half an hour to kill, go hide in a pub by the station and drink some vodka. Gawping at coins is ridiculous, considering what they just did.