Eraser can erase pencil words, which was first discovered by British scientist Priest in 1770. Before that, people wiped pencils with bread. Priest's discovery caused a great sensation because it brought great convenience to people. However, the earliest erasers were made of natural rubber. When you erase the words, there is no crumb. It just sticks the pencil tip to the eraser, and the more it is rubbed, the dirtier it gets. Later, when people made erasers, sulfur, oil and other substances were added, which made erasers easy to lose crumbs. Erased pencil crumbs leave crumbs on the eraser, so that the eraser can always be clean and the leaves will not stain the paper.