it is a difficult sensation to describe, especially if you do not have much experience in anal play.
it's sort of like using an inflatable dildo, and sort of not. the primary difference between using an inflatable
sex toy & a dogs knot is, You have NO control over a dogs penis.
lets say you got adventurous and decided to push the un-inflated sex toy into your anus, THEN decided to use the hand pump to inflate it while it's inside of you. This is a good analog for what happens with a dogs "Knot" Properly named Bulbous Glandes.
The only real difference between the two, is the dogs cock has a continuous shaft tip to root. and this is going to be VERY noticeable when your
Tied, as the Dildo has no such anchoring point.
In a nutshell, it's like someone inflated a ball inside of you, and it's large enough that you cannot easily use your abdominal muscles to "push it out".
Now, add the fact it has an anchor point that moves. now you can imagine that the "knot" and your "anus" becomes something like a "balljoint",
where either side moves in a lever like relationship. (IE: dog lowers his haunches/Dog cock INSIDE you moved "Upwards") this same motion applies to the left/right motion.
I learned from experience that you can "Break the tie", but it does take a bit of bravery because your Not used to "passing" something quite that thick.
and the sensation of doing so, can be both scary & exhilarating at the same time.
No one ever forgets their First Knotting/tie.