WARNING: The following contains spoilers for Season 2, Episode 3 of Dr. Stone, "Call From the Dead," now streaming on Crunchyroll.
Senku of Dr. Stone has a mind bordering on supernatural -- he could easily put many mathematicians to shame. While one could argue keeping track of the seconds to ensure he didn't wake up in winter is a matter of simple addition and division, the same cannot be said of Senku's latest and greatest mathematical feats from Season 2, Episode 3, "Call From the Dead."
Finally enacting the plan created in the season premiere, "Stone Wars Beginning," the team has successfully gotten a cell phone to Taiju and Yuzuriha to allow them to use Lillian's song and Gen's impression to slowly gain allies -- and immediately hit a snag. The very first person they attempt to convert, Taiju and Yuzuriha's babysitter Nikki, is a Lillian super-fan.
Knowing everything that's been made publicly available about Lillian, she has some quick questions that are difficult for the average person to fake and put Gen in quite a spot as he looks with panic to Senku. Nikki's first question wouldn't be too hard if either Gen or Senku had been fans of Lillian as well; how many CD sales has she made? At first, Gen only sees three options: guess, fake ignorance or get mad at her. Senku takes the fourth option, stunning Gen in the process -- answer correctly.
Using a process known as the Fermi Estimate, Senku takes what could be affectionately called an educated guess. Due to his love of space and some insider info from his father, he knows exactly how much a seat on the Soyuz Spaceship costs -- a seat Lillian bought. From there, he estimates that she would need to have at least twice that much money in cash, with singers of her station bringing in roughly four times that amount -- and then accounting for the fact that the publisher and stores take a cut before Lillian would receive her royalties, and then dividing that by the average cost of a CD to determine how many were actually sold -- it's a lot of numbers to have going in one's head without ever writing them down. Even so, Senku not only manages to arrive at what appears to be the correct conclusion, but he does so in less than 25 seconds.
Nikki's next question is a little more difficult -- asking for Lillian's measurements. Senku recalls a picture sent by his father that included Lillian in it -- and by using his father's height and the equipment in the background as baselines, he extrapolates Lillian's exact measurements. There's just one problem: he forgot that many celebrities doctor photos before sharing them with fans. Since his photo was from his father, who did not alter it, Nikki immediately calls out that the real Lillian would never share her real measurements with a fan, instead opting to keep the illusion of perfection -- and the jig is up.
While they're able to convince Nikki to join their cause with Lillian's song, as it's the last recording in existence, the fact remains that Senku pulled off some absolutely astounding mental gymnastics that even Homura would be jealous of if they were ever replicated into the physical world.