And referee instructors! When I did my training course some years ago, we were encouraged to take note of the players' body language and just hold back with the whistle or signal - it can sometimes help if your vision was blocked for example.
So how would you justify a sending-off in law? Denying an obvious goalscoring opportunity? No. Serious foul play or violent conduct? No.
Not condoning what Cook did as it was utterly cynical, but I probably would have done the same had I been in his shoes. But a yellow was as far as the ref...