After the boy's had mocked Percival's report of seeing the beast, by telling him no large animal could live on such a small island, Percival gave them pause for thought when he told them that the beast came from the sea.
the sea
in a cave
in a cave
Percival is unable to respond to Jack's question about the beast due to his state of shock and trauma. He only cries and cannot provide a coherent answer.
Phil & percival (pages 84, 86, & 88)
When Percival speaks, he is unable to remember where the beast comes from and becomes overwhelmed with fear. He struggles to articulate his thoughts and eventually breaks down due to the intensity of his emotions.
Percival Wemys Madison (one of the littluns) first says the beast comes from the water.
During the meeting in chapter 5 the littlun Percival Wemys Madison was asked to tell the assembled boys about the beast. Percival began to cry and once he started he would not stop, then the rest of the littluns began to join him. Maurice distracted them by pretending to fall off the springy log, which the boys called the twister. He clowned badly and rubbed his rump but he made the littluns laugh and as a result they were eventually able to persuade Percival to speak.
He says in comes out of the ocean at night. :P
The littlun with the mulberry coloured birthmark on his face spoke at the second assembly. Piggy had to kneel next to him and relay what he was saying to the rest of the boys. He mentioned seeing a snake-thing and asked what they were going to do about it and whether it would return the next night. In chapter 5:Beast from Water two littluns also spoke about the beast. Phil spoke confidently of seeing something big and horrid in the trees. The littlun Percival cried and his words were relayed to the other boys by Piggy and by Jack. He told the boys that the beast came out of the sea.
During the assembly in chapter 5 Ralph attempts to settle the issue of the beast once and for all and convince the boys that it does not exist. He has two littluns who claim to have seen it brought forward. The littun Phil's claims to have seen the beast are quickly dismissed, as it seems likely that he simply mistook Simon for the beast. Unfortunately Ralph's plan backfires when Percival Wemys Madison is told that there is nowhere on the island that a beast could hide he drops a bombshell. Speaking through Piggy and then Jack he tells the boys that the beast comes from the sea.