In the originally pitch-black cylindrical hall, as the two figures who had just crawled out of the passage entered, torches lit up one by one, illuminating the place. However, this sudden brightness was hard to adjust to. Erik squinted his eyes slightly.
In the center of the hall stood a peculiar container, a cylindrical tank almost identical to the hall's shape, sealed with metal at the top and bottom, with a circle of metal wires in the middle. Inside the tank was not a liquid, but a mechanism, which from afar resembled a balance scale.
Erik was the first to walk forward. He noticed that the cylindrical tank had a square wooden opening facing the passage. The opening was small, just large enough for a person to reach inside with their arm. Below this opening on the wooden panel was a hand-drawn image of a hand.
There was a tube at the opening, connected to the top of the balance scale inside the tank. On the right side of the scale, there was a huge metal basin. The basin was opaque, concealing its contents. At the moment, the right side of the scale was slightly tipped down, raising the left side a bit.
The left side of the scale also had some mechanisms, but they were obscured by metal barriers, making it unclear what they did. It seemed that the higher the left side was raised, the more the mechanisms could function.
Charles stood in front of the tank looking inside. There was a faint pink liquid at the bottom of the tank, most of which had drained away through pipes, leaving only some residue in the grooves at the bottom. That was clearly useless waste liquid.
"Blood," Charles said, stepping back. "It's diluted blood."
He looked up at the pipes. The inside of the pipes had some water stains; the color was very faint, but it was still discernible that the pipe once transported blood.
Erik immediately realized something. He touched the area below the square opening, feeling around. There was a drawer there, and because the light was so bright, it was easy to spot. He opened the drawer; inside were two disposable needles.
"We need to draw blood," Erik said calmly. He reached into the square opening again and indeed pulled out a tube that perfectly fit the disposable needles. It was clearly intended for blood extraction.
"The question is how much to draw," Charles frowned. "We can't use both our blood to just weigh down the scale, can we?"
"This machine has been used before." Erik attempted to touch the metal cover. Charles quickly pulled him away. "The fact that this is made of metal is probably to prevent damage through electricity."
Erik withdrew his hand. He also noticed the faint pink liquid residue at the bottom of the tank; this must have been left by washing the blood extraction pipes with water.
The fact that the right side of the scale was already somewhat lowered also suggested that quite a lot of blood had already been put in. But who could it be? How much did they give? Ultimately, how much was needed?
Charles began to ponder, "We can't be the fastest unless we didn't match with a single Batman. But I don't think that's possible. We entered the instance in the latter half of the night, which is usually Batman's peak time for rankings, so there must be at least one."
"Whether it's Batman teaming up, or Batman with Superman, or others from the Justice League, as long as Batman is involved, he'll definitely be faster than us, and very likely the first."
"Those guys are all crazy, they'd definitely be eager to give blood. Batman would probably draw quite a bit, and if Superman is there, maybe even more." Charles looked up at the blood-filled basin. "This pool might merely contain the blood of two or three people, possibly only two teams were ahead of us."
"I think you're too optimistic," Erik said. "Since it's possible to encounter Batman, it's also possible to encounter the Joker. Do you think those Super Villains would donate blood?"
"However, this mechanism didn't just appear out of nowhere. The blood donation must have a purpose, likely to help pass the game. They understand that if they don't give blood, the game might fail. Even if just to clear the game, they'd contribute some, right?"
"Moreover," Charles paused, "I think our solution to the puzzle is correct. We've used all the available tools, and we didn't get stuck. I'm not saying we're first, but we should at least be near the top. Don't underestimate yourself too much."
"There are only two needles, and they're both disposable, meaning each person can only use one once." Erik looked down at the needle in his hand and said, "I'm more inclined to have one person draw a small amount first to see what change per hundred milliliters of blood can affect the scale. Then the other person can draw as much blood as possible without harming their health."
Charles didn't respond to this but instead started analyzing on his own. "This is a game theory puzzle. The first level of game theory is among different players. Since we don't know who's involved, we also don't know how willing they are to give blood."
"But, what we don't know are the limits—how many are willing to provide more blood at the expense of their health. However, we can ensure a minimum because anyone joining the game is aiming to win, and it's unlikely they'll provide no blood at all."
"Yet, the problem is, we also don't know how much blood this mechanism requires, and no team of players knows either. If each team only needs to provide the minimal amount of blood to clear, then this puzzle would be meaningless and wouldn't suit the brutal style of the previous level designers."