said cheerfully. "Someone really does want to scare people away from the cave. That's a musical instrument called an aeolian harp, It's much the same as an ordinary harp, only the strings or wires are much thinner so that even this small breeze blowing along them can make the strings sound this sort of moaning noise. It can get really spooky when the breeze varies and blows hard and soft in turns. I've seen them used before this—in ruined castles in Germany, to give the tourists a fright. Well, it hasn't given these tourists a fright, has it?"
And the others all said, "Oh, no. Rather not," a bit doubtfully—and Commander Pott started up the engine and on they went again, hoping that that was the end of the nasty surprises and wondering all the more who it was who was trying to guard the secret of the cave and what, for the matter of that, the secret could be!
Round the next two bends they crawled carefully along with the thunder of CHITTY-CHITTY-BANG-BANG'S exhaust echoing on ahead of them. And then, all of a sudden, on a perfectly straight stretch of cave, CHITTY-CHITTY-BANG-BANG stopped dead!
"Well, that's funny," said Commander Pott, examining the dials in front of him. "We're a bit low on gas, but there's still five gallons. Oil pressure all right, engine temperature a bit high, but not more than it should be going up this sloping tunnel in third gear." And he got out to open the hood and have a look at the engine. He walked round to the front of the car and suddenly stopped. "So that's it!" he said softly. "She saw the trap!"
"What trap?" they all called, leaning out to see.
Commander Pott pointed to a very thin trip-wire stretched knee high from wall to wall across the cave.
He scratched his head and walked up and down the wire, looking at the ground in front in case there was a trap door to catch people in, and looking at the walls and the roof to see if there was some big rock or a concealed weapon waiting to drop on their heads as soon as they touched the wire. They saw him kneel down and examine where the wire joined the wall and he finally stood up and said, "Aha! The devils! I've got it!" Then he walked back to the car and got out a pair of pliers and some rubber gloves he always carried for dealing with faults in CHITTY-CHITTY-BANG-BANG'S electrical system.
"What is it?" they asked rather anxiously, because by now the whole adventure was getting almost too exciting.
Commander Pott said cheerfully, "Oh, nothing much. They're only trying to electrocute trespassers and explorers who get this far into their cave. Probably not actually kill them. Just give them a powerful shock to frighten them away. But it wouldn't have been funny if our front bumpers touched the wire. Might easily have short-circuited the whole of CHITTY-CHITTY-BANG-BANG'S electrical system as well as giving us all a nasty shock." He looked puzzled. "Funny the way CHITTY-CHITTY-BANG-BANG saw the wire and stopped just in time. There really is something almost magical about this car."
(Well, of course, Jeremy and Jemima weren't in the least surprised. They knew CHITTY-CHITTY-BANG-BANG was a magical car. Just look at the way she could fly like an airplane and skim across the sea like a speedboat. And anyway, hadn't they had their suspicions on the very first day, when they had noticed that the license plate number GEN II could be read two ways?)
Commander Pott put on his rubber gloves (electricity can't go through rubber) and gave one short snip at the wire and, sure enough, as the pliers cut through, there was a bright blue flash and a shower of sparks and the two halves of the wire fell dead.
And now, when Commander Pott got back into the driving seat and pressed the starter, CHITTY-CHITTY-BANG-BANG'S engine at once roared into life again. On they went, climbing still up the wide tunnel of the cave with the big headlights searching ahead for more dangers, and I must say that Jeremy and Jemima in the back seat were quite trembly with