What prank did Rameck play on his biology teacher?

From the text:

Rameck didn’t like his biology teacher, so he often skipped her class. When he skipped class one day, he decided to return to play a prank on her. He knocked on her door, and when she opened it, he was standing there with a can of Silly String. Without saying a word, he sprayed a web of the colorful, sticky stuff up, down, and across her face and dashed away. When she turned to face her class, the students burst out laughing. The teacher was humiliated and furious. The principal summoned Rameck to the office and suspended him indefinitely. The superintendent of the Newark public school system banned him from University High School.