According to Osho, a joke triggers huge laughter because society represses our natural joy and seriousness is rewarded; the joke provides a safe permission slip. Its structure builds alertness and inner tension, then an abrupt twist releases the coiled spring, briefly dissolving ego and returning us to childlike openness. In a truly healthy culture, laughter would flow without jokes.
A joke surprises us and gives us permission to let our bottled-up giggles burst out.