The first three minutes were agonizing. Silence. Then, whispers. Then, a sharp argument from a group near the window.

He handed each group a fat packet. “This is your Model. It contains graphs of concentration vs. time for three different reactions. As a team, answer the questions that follow. You have twenty minutes for the first three questions. Your manager will keep time.”

“No slides today,” he announced. A ripple of unease.