facehugger in original Alien

When John Hurt is lying on the table with the facehugger on his face and the helmet still on, how did the facehugger get through that small hole in the glass and attach to his face when it is 3 times the size of the hole, and they had to cut his helmet open in order to try and get it off? and if so it probably would have taken time to get to his face so how wasn't John Hurt able to stop it getting on his face? sorry if any of that didn't make sense hahaha i tried (Y)