Well, when everyone else has stopped and your lineman is still "finishing a pancake" because you coached him to "play until the whistle", it's going to look mighty obvious. In the case of our crew, we'll use our voices before throwing a flag, but some of those lineman don't listen to voices and continue action after the play. THEN they get a flag. "I didn't hear the whistle" is not a valid excuse if everyone ELSE managed to realize the play was over and had stopped action.