Theory:

     Before the meeting, the giant Makara polished his teeth with the red flowers of the tree by the river till they sparkled. Everyone was waiting for him at the meeting place.
 
     “Brothers and sisters,” he began. All the reptiles, even the beautiful king cobras, stopped talking. Makara continued his speech. “I have decided that we don’t need the tortoises! I have told them not to come today. Brothers and sisters, can you tell me why we don’t like the tortoises?”

     The reptiles looked this way and that. They felt very uncomfortable. The snakes hissed anxiously, the lizards wriggled their tails, the crocodiles opened their jaws even wider.
Explanation:
 
On the day of the Meeting, Makara Cleaned up its teeth with red flowers by the river and entered the meeting with his sparkling teeth.
 
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Makara in the river
 
This took much time that made others wait. This also shows its disrespectful attitude towards other animals, that Makara considers them below its position. On Makara's arrival, all the animals, including the snake king cobra, stopped talking and listened to Makara attentively.
 
Makara started addressing the gathering by greeting the animals as, Brothers and Sisters. It continued its speech and disclosed its plan of sending the tortoises out. This is the reason they were asked to stay away from the meeting. Though it was Makara's own decision, it has been asked to the other animals as to why did they hate tortoises? On hearing this, the other animals were really shocked. Their uncomfortable situation is reflected in their body language.
Reference:
National Council of Educational Research and Training (2006). What Happened to the Reptiles - Zai Whitaker (pp. 33-42). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.