penny dropping

• realizationGrasping what's true
• clickBrief sharp noise
• ahaExclamation of realization
• understandingMental comprehension of something
• lightbulbElectric illumination source

dawning · epiphany · coin · slot · clatter · moment · clarity · sudden · insight · comprehension · falling · metal · jingle · wishing well · arcade · piggybank · copper · recognize

• aha momentseureka, epiphany, lightbulb moment, revelation, breakthrough
• epiphaniesepiphany, aha moment, eureka, aha, lightbulb moment