Srimad Bhagavatam Canto 10, Chapter 16, Text 16

SB 10.16.16

tams tatha kataran viksya
bhagavan madhavo balah
prahasya kiñcin novaca
prabhava-jño ’nujasya sah
The Supreme Lord Balarama, the master of all transcendental knowledge, smiled and said nothing when He saw the residents of Vrndavana in such distress, since He understood the extraordinary power of His younger brother.
Sri Balarama is the plenary expansion of Lord Krsna and is thus nondifferent from Him. They are, in fact, the same Absolute Truth manifest in separate forms. According to Srila Visvanatha Cakravarti Thakura, Lord Balarama was laughing because He thought, “Krsna never cares to play with Me in My form of Sesa Naga, but now He is playing with this ordinary, mundane snake named Kaliya.”
The question may arise as to why Krsna and Balarama allowed Their loving devotees to suffer such great anguish during Krsna’s temporary imprisonment within the coils of Kaliya. It must be remembered that because the inhabitants of Vrndavana were completely liberated souls, they did not experience material emotions. When they saw their beloved Krsna in apparent danger, their love for Him intensified to the highest degree, and thus they merged completely into the ecstasy of love for Him. The whole situation has to be seen from the spiritual point of view, or it will not be seen at all.
Srimad Bhagavatam Canto 10, Chapter 16, Text 13-15
Srimad Bhagavatam Canto 10, Chapter 16, Text 17