According to Osho, the secret of a joke is the sudden, unexpected turn—the revelatory twist that subverts what the mind is predicting. As expectation builds, tension accumulates; the abrupt, absurd-yet-logical switch collapses thought for a moment, releasing energy as laughter. This stoppage of mind gives a taste of no-time, no-mind—hence a deep, meditative, even orgasmic belly-laugh.
A joke surprises your thinking so much that it stops for a moment, and that stop pops out as freeing laughter.