Ive always wondered why the super muties on the west coast have that leather looking strap that goes into their mouth. Whats that about?

Their top lip gets really fat or something so they have to put leather straps on it to hold it up. The ones on the East Coast just seem to have their top lip disappear so it looks similar.

EDIT: You can see it better on the originals

http://www.google.com/imgres?q=harry+the+super+mutant&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1280&bih=856&tbm=isch&tbnid=6h4p5JuqOtljiM:&imgrefurl=http://fallout.wikia.com/wiki/Super_mutant&docid=gcyQxz5oNxgZeM&w=640&h=480&ei=EjuKTu-rOOa1sQLp3dGSDw&zoom=1&iact=hc&vpx=595&vpy=152&dur=2578&hovh=194&hovw=259&tx=99&ty=117&page=1&tbnh=144&tbnw=193&start=0&ndsp=21&ved=1t:429,r:2,s:0

http://www.google.com/imgres?q=lou+tenant+super+mutant&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1280&bih=856&tbm=isch&tbnid=FSUVnplIh3IfgM:&imgrefurl=http://villains.wikia.com/wiki/Lieutenant_(Fallout)&docid=qcICPQdXJ9yKdM&w=480&h=247&ei=ZTuKTvfxIZOGsgKMjaEm&zoom=1&iact=rc&dur=94&page=1&tbnh=103&tbnw=200&start=0&ndsp=22&ved=1t:429,r:0,s:0&tx=123&ty=26

And the East Coast ones don't really have lips resulting in the snarl look.

http://www.google.com/imgres?q=super+mutant&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1280&bih=856&tbm=isch&tbnid=_vo5uGgmEWe_AM:&imgrefurl=http://stickfoproductions.wikia.com/wiki/Super_Mutants_(Fallout_3)&docid=HTIhaxHc_YzRCM&w=1024&h=768&ei=kzuKToi9KsymsQKfnr2oDw&zoom=1&iact=rc&dur=312&page=2&tbnh=150&tbnw=200&start=22&ndsp=21&ved=1t:429,r:14,s:22&tx=109&ty=111

Thanks for the pics, but I recall Marcus didnt have the leather strap. Would it have to do with his intelligence level?