Knock-knock. Knock knock. A pause. Knock-knock… Knockknockknock—KNOCK-KNOCK! Insulina the Insulin Molecule pounded her fist against the door in frustration. She’d tried knocking politely, ringing the doorbell, waiting a minute, and then knocking again with some more doorbell-ringing in between, but the cell simply wasn’t answering. It was unheard of. Cells always responded to hormones, otherwise they wouldn’t know what to do half the time! She looked over her shoulder to see the Glucose molecules snickering at her expense, and tried to regain her composure. She cleared her throat and tried again. “Hello, ma’am? This is Insulin Molecule Three-Four-Six on behalf…