Thats the whole point of NOT taking a head shot. You could blow off the deer jaw and wound the deer. I dont care how good of a shot you think you are, things can happen and you might not hit what you are aiming at. Why cant people understand that.
Brush in the way would be part of "if the situation is right". Of course if something was in the way that could cause deflection a head shot should'nt be taken.
A few times I have shot thru brush going for a shoulder shot to have my round deflected as much as 20 inchs. . . .broke the deers spine just forward of the hips. Once , missed a deer entirely and the brush was pretty close to the deer. . . . .Maybe it's not ethical to shoot at any part of an animal if there is a chance of the bullet deflecting of of brush and missing the vitals.