Slicing - S3D adding Triangles in Void when sliced

[jmone]

I'm trying to print this helmet from Thingiverse - https://www.thingiverse.com/thing:2886729

But as you can see from the pics, when I slice it S3D is adding some odd triangles inside the helmet. Any ideas?

Thanks
Nathan

[horst.w]

Very nice but faulty ...

horst.w
GER

[jmone]

Thanks - I'm currently trying to print as is and will remove the bad bits (have a fancy dress party next week). I'm also trying to run through various repair tools.

[jmone]

fyI Mesh mixer cleaned the worst of it up.
Thanks Again
Nathan