they only sing for an audience

Biloxi, Mississippi.  Casinos everywhere. Beautiful white sand beaches.  John takes the pups every night around 9pm for their potty walk.  There is a pond close to our RV site that they walk around and it is roaring with singing frogs (video file below).  Funny thing is, as soon as John and the pups turn their backs, the frogs abruptly stop singing.  They turn back around, they start singing again!