Ok, anyone clever enough to tell me how this effect is achieved?

programming flash
1

Click on the magazine in the middle:

https://www.rachaelraymag.com/offer/issue_cc_a/index.jsp?trkid=allrecipes_edwrr_016_va

There is a page turning effect I’d like to know how to do.

I have some ideas, but I think it’s beyond simple masking.