An Ambiguous Skull-Mask Illusion

Is this a picture of a mask looking at a skull it’s holding up for inspection, or vice versa?

I got the idea from a print by Picasso, Young man with mask of a bull, faun and profile of a woman. There’s a copy in the Art Gallery of New South Wales in Sydney, and you can see it by calling up,

search for Picasso, scroll down the results and you’ll find it!