The Ponds' Demise

So Matt Smith leaked that something in The Eleventh Hour is going to be in the final days of the Ponds. I personally think it's about the Doctor's shadow moving past the clock. I never quite figured that out. It could be the multi-form, that would explain why Amy fell asleep waiting for the Doctor when she should have been too excited to sleep. I think though, that the Doctor came back for one final mission. Another thing that I've never seen an explanation for is how the multi-form knew about the Pandorica opening and silence falling.