In ancient times, there were aliens who were good at performing strange arts. One day, in the secret room, they placed lead vinegar paper on the table. Next to it, there was a utensil, and there was a faint mist rising. This mist is the foul gas containing sulfur.

After a while, but seeing the lead vinegar paper, it gradually took a different shape. At first, only the black dots of the stars, like ink droplets on rice paper, smudged. Then, the black dots were connected and spread like spider silk, but after a while, the lead vinegar paper turned completely black.

Others were amazed when they saw it. Or asked why, the alien smiled and replied: "This is the reaction between sulfur and lead in lead vinegar paper. Sulfur meets lead, it is like a guest meets the master, and the two are on a blind date, so they become black things, so the lead vinegar paper turns black. "When everyone heard it, they realized the wonderful truth.