How does the building sink in Venice at the end of Casino Royale?

I assume that the buildings in Venice are actually built on earth and not actually floating on water, so how the heck does that building manage to sink when the inflatables are shot? And not just sink a little bit, it sinks all the way; an fast, as if the canal is about a mile deep! Is there some magical way to... show more I assume that the buildings in Venice are actually built on earth and not actually floating on water, so how the heck does that building manage to sink when the inflatables are shot?
And not just sink a little bit, it sinks all the way; an fast, as if the canal is about a mile deep!
Is there some magical way to build multi story buildings which float on unfeasibly deep canals with the aid of a few balloons to hold it up? Am I stupid? Does anyone care?
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