A ventriloquist is able to convince you that words are coming from his dummy’s mouth because the dummy’s mouth movements match the timing of the words actually coming from the ventriloquist. The ventriloquist is making use of the perceptual principle of

principle of contiguity

Explanation:

The Law of Contiguity states that after events occur together (in spatio-temporal proximity), the re-occurrence of just one of the event awakens the 'memory' of the others. It is employed in a great number of scientific theories of learning, memory, and knowledge.

in simple terms, the principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g. this is also known as upthrust.