Discovered

Rudra stared at Jhonny wide eyed as what he said made perfect sense to him. When he looked at the area from his eyes he just looked at the reef at the bottom and the footmarks of the beasts , he did not think critically enough and if it was not for Jhonny uncovering this crucial information Rudra would have still beleived that it was a natural lake and not a trap. 

The question that remained now was why would someone go to such lengths and create a lake when there was nobody present to ambush , as the one high level beast that was moving towards Rudra now was not enough to wipe the whole party out in an ambush. 

Nonetheless Rudra became extremely vigilant as he started to run his calculations In his mind at superhuman speed.

Being a mastermind himself he thought from the perspective of an attacker who set this ambush up and when he introspected why he would ever try this his heart told him that it would be for reconnaissance.