I have noticed that sows seem to squeal more than boars. Just my observation. Some make no noise, some grunt, some squeal....it just depends. I hate to make you feel worse, but you probably hit that pig. I learned my lesson early on. I was in the same situation you were in, but it was at about 15 yds and there was no way I could have missed, but I shot him on a white sand road and convinced myself that I missed cause there was no blood. It wasn't until I found a few hogs that had been shot by both slugs and arrows that didn't bleed.12 guage slugs.....no blood. That fatty skin and guts loves to seal the whole quick.I did extensive body searches and eventually found them hidden under the heaviest cover you could imagine without ever finding a drop of blood execpt where they came to rest. It was because it was so heavy that I looked there. Sometimes you can use a scent trail to get a general direction. If you get going after him right away, you can sometimes smell where he ran and gain a few yards on the search. That adrenaline will leave a real good scent trail almost like the smell of a gut shot. Strong enough that you don't need to be a dog to follow it, but a trail dog sure helps in those situations!