Dummy Not Dressed Like Mallory
Why didn't they put Mallory's dress on the dummy? Don't you think he would notice that? Also, if they were going to put a dummy down there - whey did they have to do full body cast (with a nude Mallory)? Couldn't they just do a head cast and put it on any dummy? If he wouldn't notice that the dummy/body had changed clothes, I doubt that he would notice that the body wasn't quite the right shape.
And really, if they were doing a body cast, and it was going to be covered by clothes, why couldn't she wear a swimsuit when making the cast? They showed later another girl with a stocking over her hair, so they must be able to take casts over things other than skin. Don't say because they wanted nudity, because there wasn't any shown.