Revealing mistake: The submarine is obviously a model. It's too small compared to the waves. (00:03:55)
Revealing mistake: You can see the threads moving the submarine underwater. (00:04:55)
Revealing mistake: In one scene, Titanosaurous bites Godzilla's lip and hurls him up in the air. It's quite obvious that there's no actor inside the suit, as it is much too skinny.