Here's what I have gathered over the years....
Hogs will squeal when fighting, breeding or being shot in the vitals. I have
never heard a gut shot hog squeal, although I have recovered a few hogs
that I gut shot and several that other people shot. Of those gut shot hogs
that I have recovered were shot with multi blade heads. Hogs are notorious for moving a lot on their own, and stepping forward, stepping quartering away when calm, or simply wheeling at the shot if nervous.
Multi blades through the guts will release more toxins and make the
animal sicker quicker causing them to lay down sooner. And believe me, the sooner the better when they are in the thick stuff. They will also most times leave more blood sign with a multiblade and even an intestinal trail from time to time.
If you know fora fact that you gut shot a hog or any animal for that matter, do not pursue immediately. It's best to leave them alone and let them lay down only one time. Bumping them is the worst thing you can do as there will likely be no more blood sign hardly at all when they get up leading you to nowhere if you can't follow them by their tracks. I have found a lot of them by following their tracks, and lost their track many times also as gut shot hogs want to 'run with the pack' much more so than vital hits where they are more likely to single off to themselves. 'Running with the pack' is disastrous for trying to follow a single fresh track. Then pack will also 'drag' them further away most times. Wait at least an hour, preferably two.
Hogs, that huff at you have either seen you move or heard you. They huff to see if you'll move again or make more sound. They are trying to get a bead on you and find out what you are. I have never heard a hog huff that has gotten a snoot full of my scent. They may or may not grunt when they launch to run. Hearing or seeing something has a completely different reaction than if they smell you. If they smell you, the gig is up immediately and they will put some serious distance between you and them much more so than just sound or possible sight.
Those that hear you or think they saw you will put some distance between you and them, but not as far as smelling you and they will settle down and there's a possibility of you getting on them again. However, if you do get on them again in short order, they are much more wary if they possibly see or hear you again. This second time they will put a considerable distance between you and them and the gig is likely up at this point.
Hogs talk a lot to each other. Heck, if I know what all they're saying, but
I do know that I have seen sows talk to their young ones to keep them in
line as I've witnessed this many times over the years.