Each of our cells has an energy furnace, and it is called a mitochondrion. A research team now has identified a new mode of timekeeping that involves priming the cell's furnace to properly use stored fuel when we are not eating. The interdisciplinary team has identified the "match" and "flint" responsible for lighting this tiny furnace. And the match is only available when the circadian clock says so, underscoring the importance of the biological timing system to metabolism.