Selling & the Kiosk
Players earn cash by grabbing a clam, heading to a kiosk, and holding Q to throw the clam into the storekeeper's mouth.
Confirmed verbatim by an in-game tutorial tooltip in the official gameplay trailer: "To earn cash you need to sell items. Grab a clam, head to the kiosk and hold [Q] to throw the clam into the storekeeper's mouth." Whether "the storekeeper" is the same NPC as Melvin's Shop is not confirmed.