"You... What ?"
Of course, Marty didn't resist the tentation of turning around with fish eyes. Naturally, doing so, the powder he was supposed to put in the glass landed on the table and, sadly for him, on the Letterman Jacket of the giant guy. Marty received a slap in the back of the head so hard that he went tumbling in the middle of the class, causing some students to look up from their work with astonished eyes.
"Hey, uh, sorry, didn't mean to hurt you, kid... But..."
"I... I... I'm sorry, uh... It's my fault."
"Now concentrate... Yes ?"
But Marty was so disturbed about what he just heard that he couldn't manipulate the chemicals the correct way. After a good minute of trying, the russian took the bottle from his hands and finished the assignment faster that anyone in the class could.