I have to agree with the others a "hostile force" is not something that sends a shiver down your back or a case of heart burn. As it is a will save i would guess it is more like a headache that suddenly comes on and just as quickly goes away. Which is not normal. Now as to going after the stranger in front of me, no I might now, depending on the mooks int.

It would depend on the situation the mook was in. A man standing in front of me waving his hands and chanting, yes I would think he did it, a man standing in front of me staring hard and maybe talking at me in a strange lang yes. Remember as said above a silent/still spell still Provokes an attack of Opportunity.

So let me see I got this headache suddenly that came and went and this man is staring at me really really hard, so hard I could slap him and he would not stop me. Yea he is up to something.

Now if there was 2 or 3 people standing around, maybe the mook might not notice the stare or if the mook had a low Int yes. But at times it is perfectly normal for mooks to react.