Mine seems to vary from a barely perceptible nudge, to, as happened last week, a pretty vigorous turn to the right. It's always a turn to the right, never the left, something that's puzzled me with one road junction where this happens regularly. The junction looks like this (very rough sketch!):
View attachment 641609
The lane on the left is single track, but slightly wider right at the junction. If there is a car waiting to pull out (the blue arrow) then my car (the red arrow) will always, without fail, sound the alarm, brake hard and try to steer to the right, often quite vigorously, but equally often sometimes a barely perceptible nudge. It does always brake hard, pretty much a full on emergency stop if I didn't hit the accelerator quickly to cancel it. It's done it several times at this exact spot, but only ever when there's a vehicle waiting to pull out from the left. If that side junction is empty there's no indication on the screen in the car that anything unusual has been detected.
My theory is that the car initially mistakes the side road for the road I'm driving on, then detects the car in that road as a threat (which it would be if I was to barrel into it at ~40mph). It would be interesting to see the underlying FSD "picture", as the videos I've seen of that do suggest that there is a fair bit of jitter, as the system refines its interpretation of what the cameras and radar are detecting.