The day was to consist almost entirely of things we had not been expecting, starting with the arrival of a group of about two dozen American tourists on a specially chartered boat. They were mostly of early retirement age, festooned with cameras, polyester leisure suits, gold-rimmed glasses and Mid-Western accents, and I didn't think that they would be sitting up a tree all day either.

We were severely put out by their arrival and felt that the last vestige of any sense of intrepidness we were still trying to hold on to was finally slipping away.

We found a guard and asked what was going on. He said we could go on ahead now if we wanted to avoid the large party, so we set off with him immediately. We had a walk of about three or four miles through the forest along a path that was obviously well prepared and well trodden. The air was hot and dusty, and we walked with a sense of queasy uncertainty about how the day was going to go. After a while we became aware of the faint sound of a bell moving along ahead of us, and quickened our footsteps to find out what it was. We rounded a corner, and were confronted with some stomach-turning reality.

Up till now there had been something dreamlike about the whole experience. It was as if the action of walking through the archway and ingesting the musty odour of the island spirited you into an illusory world, in which words like 'dragon' and `snake' and `goat' acquired fantastical meanings that had no analogue in the real one, and no consequence in it either. Now I had the feeling that the dream was slithering down the slope into nightmare, and that it was the sort of nightmare from which you would wake to discover that you had indeed wet the bed, that someone was indeed shaking you and shouting, and that the acrid smell of smoke was indeed your house incinerating itself.

Ahead of us on the path was a young goat. It had a bell and a rope around its neck and was being led unwillingly along the pathway by another guard. We followed it numbly. Occasionally it would trot along hesitantly for a few paces, and then an appalling dread would seem suddenly to seize it and it would push its forelegs into the ground, put its head down and struggle desperately against the tugging of the rope, bleating and crying. The guard would pull roughly on the rope, and swipe at the goat's hindquarters with a bunch of leafy twigs he was carrying in his other hand, and the goat would at last tumble forward and trot along a few more paces, light-headed with fear. There was nothing for the goat to see to make it so afraid, and nothing, so far as we could tell, to hear; but who knows what the goat could smell in that place towards which we all were moving.

Our deeply sinking spirits were next clouted sideways from a totally unexpected direction. We came across a circle of concrete set in the middle of a clearing. The circle was about twenty feet across, and had two parallel black stripes painted on it, with another black stripe at right angles to them, connecting their centres. It took us a few moments to work out what the symbol was and what it meant. Then we got it. It was just an `H'. The circle was a helicopter pad. Whatever it was that was going to happen to this goat was something that people came by helicopter to see. We trotted on, numb and light-headed, suddenly finding meaningless things to laugh wildly and hysterically at, as if we were walking wilfully towards something that would destroy us as well.

Leading from the helipad was a yet more formal pathway. It was a couple of yards wide with a stout wooden fence along either side about two feet high. We followed this along for a couple of hundred yards until we came at last to a wide gully, about ten feet deep, and here there were a number of things to see.

To our left was a kind of bandstand.

Several rows of bench seats were banked up behind each other, with a sloping wooden roof to protect them from the sun and other inclemencies in the weather. Tied to the front rail of the bandstand were both ends of a long piece of blue nylon rope which ran out and down into the gully, where it was slung over a pulley wheel which hung from the branches of a small bent tree. A small iron hook hung from the rope.

Stationed around the tree, basking in the dull light of a hot but overcast day, and in the stench of rotten death, were six large, muddy grey dragon lizards.

The largest of them was probably about ten feet long.

It was at first quite difficult to gauge their size. We were not that close as yet, the light was too blear and grey to model them clearly to the eye, and the eye was simply not accustomed to equating something with the shape of a lizard with something of that size.

I stared at them awhile, aghast, until I realised that Mark was tapping me on the arm. I turned to look. On the other side of the short fence, a large dragon was approaching us.

It had emerged from the undergrowth, attracted, no doubt by the knowledge that the arrival of human beings meant that it was feeding time. We learnt later that the group of dragons that hang out in the gully rarely go very far from it and now do very little at all other than lie and wait to be fed.

The dragon lizard padded towards us, slapping its feet down aggressively, first its front left and back right, then vice versa, carrying its great weight easily and springily, with the swinging, purposeful gait of a bully. Its long, narrow, pale, forked tongue flickered in and out, testing the air for the smell of dead things.

It reached the far side of the fence, and then began to range back and forth tetchily, waiting for action, swinging and scraping its heavy tail across the dusty earth. Its rough, scaly skin hung a little loosely over its body, like chain mail, gathering to a series of cowl-like folds just behind its long death's head of a face. Its legs are thick and muscular, and end in claws such as you'd expect to find at the bottom of a brass table leg.

The thing is just a monitor lizard, and yet it is massive to a degree that is unreal. As it rears its head up over the fence and around as it turns, you wonder how it's done, what trickery is involved.

At that moment the party of tourists began to straggle towards us along the path, cheery and unimpressed, wanting to know what was up, what was happening. Look, there's one of those dragons. Ooh it's a big one. Nasty looking feller!

And now the worst of it was about to happen.

At a discreet distance behind the bandstand the goat was being slaughtered. Two park guards held the struggling, bleating creature down on the ground with its neck across a log and hacked its head off with a machete, holding the bunch of leafy twigs against it to staunch the eruption of blood. The goat took several minutes to die.

Once it was dead, they cut off one of its back legs for the dragon behind the fence, then took the rest of the body, and fastened it on to the hook on the blue nylon rope. It rocked and swayed in the breeze as they winched it down to the dragons lying in the gully.

The dragons took only a lethargic interest in it for a while. They were very well fed and sleepy dragons. At last one reared itself up, approached the hanging carcass and ripped gently at its soft underbelly. A great muddle of intestines slipped out of the goat and flopped over the dragon's head. They lay there for a while, steaming gently. The dragon seemed, for the moment, not to take any further interest.

Another dragon then heaved itself into motion and approached. It sniffed and licked at the air, and then started to eat the intestines of the goat from off the head of the first dragon, until the first dragon rounded on it, and started to claim part of its meal for itself. At first nip a thick green liquid flooded out of the glistening grey coils, and as the meal proceeded, the head of each dragon in turn became wet with the green liquid.