How and Why to replace the Anode rod of a hot water heater

This guy's no Rich Trethewey, but he does a good job showing how to change an anode in a far tighter space - with the hot water heater actually installed as opposed to Rich's magic 'in the middle of my shop' heater.

This video kicks Rich's hiney in terms of the science explained. I love the test for electrical conduction at 2:50. It's a neat little check to show us that the cell ACME is in place. This video also goes into far more of the chemistry of corrosion from about 3:30 onward, especially writing the reactions for the oxidation of iron. I would've never thought of using an electrically powered anode for a hot water heater. I wonder where that might be required.

By the way, has anybody ever heard the phrase (from 1:22) that two things can be lying "side by each"?