This clip is a fun illustration of the quantum weirdness of the double-slit experiment. Be warned, however! The movie this is from, Quantum Weirdness! What the BLEEP Do We Know!?, is a mélange of pseudoscience and quantum physics. This clip holds together pretty well until the end, when it starts to posit that a conscious observer alters reality.
The “observer” here need not be conscious – it is the act of measurement that collapses the wave function. The physics of measurement, of actually determining which slit the electron went through, causes quantum decoherence in which the vastly entangled quantum system assumes a given state. When you don’t have the “observer” present the quantum state remains entangled and superposition can occur and create an interference pattern.
And if all of that sounds like mumbo jumbo, well, what the BLEEP do we know?