CC Madhya 15.11

“yo ’si so ’si namo ’stu te” ei mantra paḍe
mukha-vādya kari’ prabhu hāsāya ācāryere
Synonyms: 
yaḥ asi — whatever You are; saḥ asi — so You are; namaḥ astu te — I offer My respects unto You; ei mantra paḍe — chants this mantra; mukha-vādya kari’ — making a sound within the mouth; prabhu — Lord Śrī Caitanya Mahāprabhu; hāsāya — causes to laugh; ācāryere — Advaita Ācārya.
Translation: 
Śrī Caitanya Mahāprabhu would worship Advaita Ācārya by chanting the mantra “Whatever You are, You are — but I offer My respects unto You.” In addition, the Lord would make some sounds within His mouth that would make Advaita Ācārya laugh.