Agnipurana 341.9

341.9

śṛṅgāraṃ dvividhaṃ vidyādvāṅnepathyakriyātmakam /
hāsaś ca turvidho 'lakṣyadantaḥ smita itīritaḥ //

One should know laughter to be twofold: consisting of speech, costumes, and action. / Laughter is of four kinds; when the teeth are invisible, it is called a smile (smita);