pravistah somam apibac
candrarkabhyam ca sucitah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Rahu, the demon who causes eclipses of the sun and moon, covered himself with the dress of a demigod and thus entered the assembly of the demigods and drank nectar without being detected by anyone, even by the Supreme Personality of Godhead. The moon and the sun, however, because of permanent animosity toward Rahu, understood the situation. Thus Rahu was detected.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Supreme Personality of Godhead, Mohini-murti, was able to bewilder all the demons, but Rahu was so clever that he was not bewildered. Rahu could understand that Mohini-murti was cheating the demons, and therefore he changed his dress, disguised himself as a demigod, and sat down in the assembly of the demigods. Here one may ask why the Supreme Personality of Godhead could not detect Rahu. The reason is that the Lord wanted to show the effects of drinking nectar. This will be revealed in the following verses. The moon and sun, however, were always alert in regard to Rahu. Thus when Rahu entered the assembly of the demigods, the moon and sun immediately detected him, and then the Supreme Personality of Godhead also became aware of him.