Biological processes are complex.
Really. Really. Complex.
These fancy biochemical transformations follow reaction pathways that are the handiwork of selective evolutionary pressures and their cumulative influences over a relative infinity of time…
What is especially striking about these pathways is their intricacy. Often they are guided along a chain of events, a series of indirect actions cascading towards a specific chemical end, the final domino.
Here’s an example:
The body’s chemical response to caffeine
The physiological benefits of caffeine spring into action through an indirect series of chemical responses to the initial absorption of caffeine into the small intestine.
Caffeine competitively inhibits phosphodiesterase, the enzyme that degrades cyclic AMP. This increase of cyclic AMP usually mediates most of the pharmacological actions of caffeine. This is due to caffeine’s structural similarity with adenosine. By blocking the degradation process of cyclic AMP, caffeine indirectly affects regulation of cAMP-dependent protein kinases, which are responsible for the regulation of glycogen, sugars and lipid metabolism. In addition, it stimulates the release of hormones, in particular: epinephrine (adrenaline). 
The Rube Goldberg machine is an irresistible analogy for these chain reactions. I like to think (I do like to think) that the Rube Goldberg machine is a meditation on causal ingenuity. These “machines” link disparate events (such as a piece of paper catching fire and a bucket of water being filled) by physical causation. Anyway, I wanted to share one of my favorite Rube Goldberg set-ups below. Surfactants oozing down a plank! Exploding balloons and wheelbarrows! Fire!
The entire sequence is a thirty-minute feature. Yes, they got it to go for as long as you sit in your evening commute or devote to preparing and consuming a breakfast burrito… You can see the entire video at the Institute of Contemporary Art in Boston (which is where the 250th American Chemical Society meeting is being held, and where I am currently tippity-typing from.)