Solution
Option 1 -> While the snake disappeared, the passage doesn't explicitly state it left for a safer haven away from civilization - it simply couldn't be found.
Option 2 -> They cleared the overgrowth as part of their search strategy to find the snake, not as the reason the plan failed - this was their attempt to locate it.
Option 3 -> Though mother agreed with the beggar's religious sentiment, there's no indication she stopped the hunt - they continued searching and even called the snake-charmer.
Option 4 -> The snake-charmer explicitly stated: "If you show me the snake, I'll at once catch it. Otherwise, what can I do?" and then departed, leaving them helpless.
Hence, Option 4 -> The passage clearly shows the snake-charmer's helplessness was the turning point - he needed to see the snake to catch it, but they couldn't locate it to show him. After he left, they continued searching until 5pm before finally giving up. His inability to help without seeing the snake directly caused their plan to fail -> correct