题目内容：
A long time ago, Milton S. Hershey, the creator of the popular chocolate bars, was dipped in warm chocolate. I know all about it. My grandfather was there! At nineteen, Hershey established a candy business in Philadelphia. Although it failed, he tried again in several other cities and succeeded with Crystal A Caramels. But Hershey was not content. He began experimenting with chocolate and managed to sell his first chocolate bars in 1900. They were an instant success. In 1903, Hershey built a factory.
Hershey was usually pleasant and kind and enjoyed a good joke. However, in his chocolate factory, he held high standards for all the workers. He was both respected and feared. His anger would burst out when things didn’t go as he’d expected, and workers were fired for mistakes.
My grandfather began working in the factory as a young man. His job was to push the vats （大桶） of warm chocolate to a storage area. To do this, he had to push the heavy vats up a ramp （斜坡） and across the walkway. One day, Hershey was walking backward on the walkway while my grandfather was pushing a vat of chocolate up the ramp. Bump. Clunk. Ker-plop! Hershey fell backward into the vat. Everyone else held their breath and ran up to pull him out. Grandfather froze in fear. Was he going to lose his job?
Hershey stood stiffly with his hands on his hips. Color rose in his face. He said something in a low voice. Then he smiled. “It’s not your fault, son,” he said. “I need to watch where I’m going.” He put some chocolate in his mouth. “Mmm, that’s good,” he said. Everyone laughed. The tour continued, with Hershey dripping chocolate as he went. And Grandfather kept his job.
What did Grandfather do in Hershey’s factory? （回答词数不超过12个）
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