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I've beaten 2 of Bismuths arm things. I think judgement was the second one.

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You flip the switch. One of the smaller vessels starts churning, and thin streams of molten liquid flow from both it and the large smelter to combine in another vat. There's some more shaking and banging, and then the product is disgorged into the main channel.

The monsters immediately burst to life, swarming the metal like starving animals. They crawl and wriggle all over it, constantly poking and prodding even as they work it into a new shape. When they're done, you're delighted to see they've produced a new conveyor!

You pull the lever down, and the ground falls out from under the new conveyor! It drops into what appears to be a vat of water, which immediately froths into a boil. The conveyor rises again, steaming but cooled into a solid shape. But it's not over yet. The monsters keep running their fingers over the metal.
With a viciousness that startles you, one grabs a small hammer and slams it down hard. The arm-monster recoils from the impact, and the new conveyor appears unblemished.

"Oh, I see!" Pearl says. "Adding vanadium increased the hardness of the metal. How fascinating!"
The monsters take a small piece out of the stream and begin doing… something with it. First one squeezes it between its thumb and forefinger, and after a few seconds of that, two grasp one end each and try to pull it apart. To your relief, they don't succeed.

But then for some reason they keep pulling and prodding at the new conveyor – really hard, too! It looks like they're trying to break it!
And they do. As they try to bend it, the whole thing snaps in half. They throw the ruined pieces into the lava.
You wail and tug at your hair as you watch the new conveyor melt into slag. What was wrong with it? You'll just have to try again!