Charge phone to full 100%. Turn it off.
Put it into a faraday cage, e.g. a steel box, for 7 days.
Take it out again and wonder why the battery is empty.
(The faraday cage has the effect of making the modem have to switch bands constantly, which costs more electricity than sleep mode in LTE)
Repeat the experiment a few times. Then cross over: liberate the caged phone, cage the free phone, and repeat the experiment a few more times. Or alternate the phones' positions between experiments. This mitigates hardware and software differences that might've been overlooked (such as a faulty battery, etc).
Analyze the results, draw your conclusions, publish, and encourage others to reproduce.
And the reason is exactly the finish. Metal and plastic spoons, forks, lids, etc. are nice and smooth and don't get in your way. Cheaply made wood or cardboards ones are rough and tacky.
Of course you could argue that from an environmental standpoint, that's not a bug but a feature: now I'm using even less disposable stuff (first, no plastic because it's been replaced by other stuff; and second also the replacements because I hate using them).