So I would appreciate any insight on a behaviour that I have seen amongst my dogs.  It is not a new thing but we had a prolonged episode this morning which made me wonder what on earth is going through their minds.

First a little background

Lola is my rescue irish beagley hound.  She is 3 at some point this year and I have had her from being about 6 months.  Typical hound, loves other dogs and craves company (and food) very sweet natured girl and certainly not top dog, nor would she want to be!  She is neutered.  High energy dog.

Roxy is my little springer, 19 months who I have had from 7 weeks.  She is a working type and loves to have a job to do (fetch is as good as any).  She is not neutered yet and apart from the occasional spat when she has a phantom and feels the need to guard whatever is her baby for the day she and Lola get on great.  Of the two I would say she is the more dominant.  However when it comes to other dogs she is ultra submissive, almost to the point of being fearful.  Not a lack of socialisation, just who she is.  Again high energy dog

Madison is my housemates 6 year old staff x.  She has lived with us since July of last year.  She is neutered.  She has been with her owner from being about 10 months old.  She is a typical staff in how she plays with the other two, very bouncy and bubbly.  She tends to play quite rough and be quite dominant with my two but neither of them bothers too much about that.

The three of them get on great almost 100% of the time, Roxy has her hormonal moments and they all have their own spaces where they can go if they want.  We almost never have a real falling out.  They play a lot together, some of it rough housing some of it just generally racing about.  They sleep in a big heap together and eat together but don't share.  although if it is a treat or pilfered food they will share!

So we come to the "problem", it is not really, more just an oddity.  Madison when playing will bite heads and throats (gently no squeaks or anything).  This is usually when there is a lot of rough housing going on.  The other two are never injured in all of this and generally play will continue.  If myself or my housemate is worried about the level getting to much we do ask them all to chill out and step in to stop it. 

When Madison bites Roxy's head it seems to do something to her and she becomes absolutely demented excited, and will wriggle and wiggle on her back or belly and incite her to do it more.  Her tail wags like mad.  This morning we were all upstairs and they were doing it at the top of the stairs Madison would stop Roxy would come running round the back of me like a demented fool then go wriggling herself back as if to say "Do it again".

Now it's not a massive issue as there are no injuries but what on earth is going on in my Roxy's brain that makes her enjoy this so much.  It is quite hilarious to watch.  It is not a recent thing, they have always played this way.  I will admit that the sun being out and Roxy having decided that she does not have any babies to worry about since the weekend has helped to add to the dementedness this morning but why does she like it so much?

I didn't want to read and run as you've not had many ideas.  Here's mine for what it's worth.
I think Roxy's behaviour is appeasing the top dog rather than excitement.  Sort of, thanks for not eating me?  My springer is the same if my top bitch invites her to play.  She goes totally over the top with excitement that she ends up getting herself into bother.  And She is exactly how you described yours.  I think the head squeezing and throat grabbing is a top dog asserting herself and Roxy is just falling into line under her in the pack order.
That said, I wouldn't particularly allow this behaviour.  I don't allow any of my dogs to assert themselves in this way too much.  I like to pretend I am the boss!lol

Two of my dogs play like this all the time - I have never had a problem with it although it looks quite scary at times as the large dog can fit the whole of the small dog's head completley inside his mouth. It just seems a normal part of their play with those two particular dogs - the smaller dog wages guerilla warfare on the larger one and grabs any part of him he can as he flies past.

Thanks for your input folks, I have to be honest I am not too worried about it.  If it ever looks like it is getting a bit much I can soon stop it.  In fact today Roxy was definitely trying to instigate it so I really don't know what is going through her head although I am inclined to agree it is probably at least partly an appeasement but she definitely gets very revved up about it.  She is a strange one and clearly one on her own!