It looks like a Triple Overhand Noose to me.
Yep, that looks about right. Below is one I whipped up in 7/64 Amsteel Blue. Difference is with a noose, there are 2/3 loops, depending on how you look at it, under the wraps with the tail of the coils going through one of the loops to terminate. This brings the tail out 90 degrees to the standing/working part of the rope. You can see that in the link below.
http://www.wikihow.com/Tie-a-Hangmans-Noose
In this post from the link Alex posted...
http://www.ifish.net/board/showpost.php?p=2777444&postcount=22
You can see what appears to be the closest representation of the knot MP uses. Which simply put is a triple overhand knot tied back over itself rather than down the working part of the line. Its done this way to create the loop rather than just a stopper knot.
Anitmated... double would be 2.5 wraps, triple 3.5 etc.
http://www.animatedknots.com/stopper/index.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com
To begin with, yes. But as you pull the knot MP uses, it will cinch around the line and make it difficult to get it to slip. And as LandyAndy stated, it will only slip towards the thimble or eye as you load the working part of the line.
