According to Osho, laughter in Zen cuts through seriousness and the doctrinal mind; Zen people laugh twice: first spontaneously, then at their own laughter, so the ego and solemnity dissolve. This non-serious sincerity opens a gap of no-mind, bringing you here-now, like Buddha's wordless flower or 'Look at the cypress.' Laughter becomes meditation's flavor: immediacy, authenticity, and presence.
Laughing makes you stop being too serious, drop your busy thoughts, and just be honestly here now.