I have noticed that a "strike" position always entails some quivering, as their muscles are all tensed up and their heads and necks kind of "shake" a little, just before they strike. Like when you tense up your arm really, really hard, and your arm shakes a bit.
If they are in an s-shape neck, but they are not TENSED up with their muscles, they have always been docile at that point. I have only one hatchling that won't let me handle him yet, and he always tenses up and gets all S-S-S sss ed up with tense muscles whenever I check on him. He strikes at anything anywhere near his face, lol. I have named him Snappy.