Like a rock. Even a .22 LR behind the ear will drop them. Just don't look for it do do any real damage on a body shot.
+1 In a pinch, I dropped a feral hog where he stood with a .22WMR at 60-70yds. In behind and below the left ear, out behind and below the right ear. It doesn't get any cleaner than that.
.243 with expanding bullets can make a mess of that same shot: The one I got later could have been completely gutted through the exit wound.