After Elliot gets out of the pool after hearing Rebecca's voice, and gets his mother, when she comes out to check the pool, Elliot's wet footprints by the pool disappear and reappear between shots.
Right after Eve rescues Elliot from under the pool cover, it seems to be rolled up on its own. Even though it had been too difficult to move with two people just moments before."
Eve uses a very long hose to breathe underwater. It is impossible to breathe this way without a compressor pumping air into the hose.