SB 3.23.20

haṁsa-pārāvata-vrātais
 tatra tatra nikūjitam
kṛtrimān manyamānaiḥ svān
 adhiruhyādhiruhya ca
Word for word: 
haṁsa — of swans; pārāvata — of pigeons; vrātaiḥ — with multitudes; tatra tatra — here and there; nikūjitam — vibrated; kṛtrimān — artificial; manyamānaiḥ — thinking; svān — belonging to their own kind; adhiruhya adhiruhya — rising repeatedly; ca — and.
Translation: 
Here and there in that palace were multitudes of live swans and pigeons, as well as artificial swans and pigeons so lifelike that the real swans rose above them again and again, thinking them live birds like themselves. Thus the palace vibrated with the sounds of these birds.