The figure paused and turned back to Jessica. She made no attempt to answer the question either with words or gesture. She was too scared to.

‘I hadn’t,’ the figure said. ‘Hot potting is when people go for a dip in a thermal spring or a geyser. Apparently it’s quite a thrill. Yellowstone is famous for springs and geysers, if you didn’t know. The whole point though, is that this area of the park was off limits for a good reason. Those springs weren’t created by Mother Nature as a reward for eager tourists. They’re unforgiving and deadly. The temperature of the water can be close to boiling, and it’s often very acidic.

‘Anyhow, the poor chap goes to dip his toe to test the water. He slips, he falls. What happens? He gets boiled and burned alive by that hot acidic water. His companion is there, filming the whole thing on her mobile phone, their perfect getaway taking quite an unexpected turn.’

The figure pulled out Jessica’s small leather purse and stepped to the large glass jar sitting at one end of the worktop. The figure put on a heavy-duty rubber glove and lifted the lid off the jar, which was half-filled with liquid.

‘The man was dead within seconds. He had absolutely no chance of survival. The friend raised the alarm immediately but due to a turn in the weather, the rescue team couldn’t even attempt to recover what was left of him. When they returned a day or two later, do you know what they found?’

The figure turned to Jessica and waited for a response. Once again no words passed her lips.

‘They found absolutely nothing. No trace of the man whatsoever. No skin, no flesh, no bones, no teeth, no clothes. The acid had dissolved him. Whatever atoms used to be a man were just part of that deadly acidic mixture.’

The figure took the purse in its gloved hand and lifted it towards the jar.

‘And remember what I’m talking about there is just a natural mixture of water and acid from dissolved rocks. Imagine how much more powerful a heavily concentrated and deliberately manufactured substance could be. Imagine what that kind of substance would do to a human body.’

The figure moved the purse down inside the jar and the outer edges of it touched the liquid which sizzled and bubbled. Jessica began to shudder and tremble with fear. She felt her bladder release, began to whimper and plead, incoherently.

Carefully, the figure dropped the purse into the jar and placed the lid back on top. The acid fizzed and frothed ferociously as it worked on devouring the leather, fabric and plastics that had been thrown its way.