Scorpio
Armchair Expert
From what I heard of the verbal stoush between he & Johnson afterwards, Proctor was saying Johnson was choking him, so I think he meant Johnson's arm was squashed against his nose so he couldnt breathe, hence he opened his mouth to get oxygen in.
If Johnson is applying pressure to his mouth, then if Proctor opens his mouth, the arm goes further in... but if he closes his mouth it's a bite
Lose-lose