Nothing happens
He told them that they needed to see it with their own eyes, this manta ray was dangerous at all, it was very friendly. His parents were skeptical if Peter had even seen the manta ray in the first place, but they followed him back to the pier to see anyway.
Once they got there, they didn’t know what was going to happen. Peter sat by the steps again, through some pebbles into the water, and waited. They waited for a few minutes but nothing was happening. Peter couldn’t understand it, he was sure that the pebbles attracted the manta ray, just like last time.