The plant must have sensed the movement of many animals and so, it knew that today must be the 'monthly feast'.
Usually, the water lilies would never target the same prey to avoid infighting, but if the other party just wanted to hunt the animals who came with another man-eating water lily, both sides tacitly cooperated.
Anyway, this month, it was the turn of the controlled water lily to hunt foreigners, so the other water lily came just to hunt some animals who came to the 'party'.
But its movement definitely aroused the attention of many other monsters and beasts around, so while the first lily came from the left side of the boat, the other came approached to the right side of the boat with a mighty 'army' under the water!