What else would make a hog run?

I think hogs somehow know when they are safe and when they need to haul a$$. For instance few wks ago we pulled up to place to hunt an low an behold I seen a few hogs an I'm prob 200 yds away an I keep drivin an try to be quiet while getting dogs collared an ready an I walk back to pipeline wher I see them and they done scattered. Dogs ran them for over an hr an never caught one. Another example I was riding around lookin for sigh one day an I'm drivin down the road an spot hogs in middle of road 75yd ahead of me and they could clearly see my truck. I sat ther an watched them for. 20min feed in the ditch. And of course I had no dog with me. So they know when they are in danger whether a dog is barking or not. Around here if they hear a tailgate drop there probably already on there way out