It really feels amazing, providing the dog does not use it's teeth on your ass, and nibble while licking. That really hurts. Been there and had it happen.. The dogs tongue, some of them are long, and if you are able to completely relax your rectum muscles for the dog to get it's long tongue deep inside of you, and able to lick your prostate, it is totally heaven. Drives you over the edge in no time. I've had an idea dog, 102 pounds Malamute that knows how to do it. Been doing it with him now for 11 years. Going to miss it when he passes away. The only dog I have ever had out of countless dogs that has done it. He has licked me for as long as 45 minutes, non stop. At some point you kinda go numb down there, and just relax, as he drives his tongue in and out of your ass, over and over like he is licking a juicy steak. They do make your rectum bleed, and the taste of fresh blood drives the dog wild. It heals up, and do it again, heals up, and over and over. Some times I have done it day after day, other times I wait a few days.
Hope this helps you out in what you are wanting to know ?