I must apologise in advance, because this is a really silly oneshot. It's based on this line in the ACD short story Charles Augustus Milverton:

"Do you feel a creeping, shrinking sensation, Watson, when you stand before the serpents in the Zoo, and see the slithery, gliding, venomous creatures, with their deadly eyes and wicked, flattened faces?"

I couldn't imagine Sherlock Holmes ever frequenting a zoo, so I wrote this oneshot, in which the detective's modern incarnation is dragged rather unwillingly to such an establishment.

It came as a shock to John Watson to discover that his flatmate had never once in his life set foot in a zoo. He thought that everyone must have been to a zoo at some point. He could remember being dragged around various wildlife institutions when his parents wanted to take their children on a cheap day out. It had got him interested in biology, though, which admittedly had led him down a rather different path, but it was a start.

Anyway, he had happened to mention one of these visits, and Sherlock had said offhandedly that he'd never gone to the zoo.

'What, where did your parents take you on days out?' John asked.

'Museums...' Sherlock shrugged. 'I spent half my childhood in the British Museum, and the other half in the Ashmolean.'

It occurred to John that this evidently didn't do him much good. Sherlock's knowledge of many things that were surely covered by these museums was laughable. Perhaps he hadn't paid attention.

But it was this comment that aroused pity in John, and he resolved to give Sherlock a second chance at an interesting childhood as soon as he could. After all, though he would never admit it, the detective was in everything but age just a tall, supremely intelligent child.

'C'mon then,' said John one Saturday morning, after his elevenses cup of tea and cheeky biscuit. He made to get out of his chair, but was halted by a naïvely bewildered glance from Sherlock.

'Where are we going?' asked Sherlock.

'Oh,' replied John. 'I thought you might have deduced it by now.'

'Oh God,' said Sherlock, 'you're taking me to the zoo.'

John tried to grin, but just ended up looking a bit embarrassed. 'Problem?'

'A thousand of them,' Sherlock groaned. But, to John's surprise, he dragged himself to his feet and went to get his coat; and a minute later they had hailed a taxi and were on their way.

It only occurred to John at the gates of the zoo that two middle-aged men wandering round without children in tow would look a bit odd. He wondered, not for the first time, if he could pass Sherlock off as being his mental age, that is about twelve. But for now nobody seemed to have noticed, and so they paid and started to inspect the enclosures.

'I'm bored, John,' Sherlock complained after two seconds of watching a flamingo doing nothing.

'Well, look at a different bird then,' John replied, indicating a number of ducks by the edge of a small man-made lake, all of which were similarly doing nothing.

'But it's all boring,' Sherlock said.

John glanced sideways at him, a little nervously. It wasn't impossible for Sherlock to have brought his gun with him and to start shooting things. But he couldn't see the shape of his pistol underneath his coat, and so sighed with relief. Being arrested would rather ruin their day out.

The next exhibit was a selection of primates, most of them screeching and running around in enclosures filled with branches and shelves and things. John seemed mildly interested by them. Sherlock didn't.

'Look at this,' said John, pointing to one of the interpretation boards. Sherlock tore his eyes away from a bonobo with which he had been having a staring competition. 'According to this, bonobos are really closely related to humans, but not as much as chimpanzees. It says that if we were more like bonobos, we'd be a much more peaceful species.'

'That would be boring,' said Sherlock simply, and walked off towards the tropical house.

When John joined him, he was staring at a giant spider. The notice next to the cage proclaimed them to be camel spiders, native to the Middle East. This specimen was large, sand-coloured and hiding under a rock. John could not help but shudder a little.

'I saw some of those in Afghanistan,' he said. 'Horrible creatures.'

Sherlock looked sideways at him. 'They're not dangerous.'

'Well, I know, but spiders aren't that appealing in general,' John shrugged.

Sherlock was indifferent. He didn't mind spiders. Mostly because he could never be bothered to do anything about them when he saw them in the house. They weren't worth leaving his armchair for. 'I can't be scared by a thing that would harm me only in self-defence.'

'What does scare you?' asked John.

He had meant it as a rhetorical question, but it was at that moment that Sherlock drew his attention away from the spiders and looked in the next cage.

'Those,' he said in a small voice.

The cage contained a number of green snakes, all of which seemed to turn as Sherlock and John approached them. One of them flicked its tongue at them.

'You're scared of snakes?' John said incredulously. He couldn't believe Sherlock had ever come across that many snakes. He had seen a few himself on his travels – had treated some nasty snake bites, indeed – but he didn't much mind them.

'I hate snakes,' said Sherlock, Indiana Jones-style. Despite his obvious fear, however, he pressed his nose against the glass, and looked more closely at his enemy.

'Trying to set it free?' asked John in a joking sort of fashion, dropping in the Harry Potter reference even though Sherlock had never read Harry Potter.

Sherlock just looked a bit confused, and continued his staring contest with the snake. 'Look at their eyes, John. They're malicious... Horrid animals. Spiders are stupid. Snakes have the intelligence of a villain... Their eyes remind me of...'

What snake eyes reminded Sherlock of, John would never know, because Sherlock did not dare to finish his sentence; but he could very much guess. He had seen such sly malice as Sherlock described in the eyes of many a foe, in Afghanistan and England equally. He suddenly understood why Sherlock hated snakes, if he saw such a vile expression in their eyes, and was reminded of the terrible villains he had come up against.

'Why don't we go and see the tortoises?' John suggested.

Sherlock's fear seemed to have created a deep fascination, and it was a good few moments before John could tear him away to look at the rest of the animals. Sherlock then returned to being rather bored, and did not speak until they emerged and John bought him an ice-cream, as if he was a child.

'I'm sorry; that was a bad idea,' John said as they were leaving the place. He was referring, of course, to coming to the zoo in the first place.

'It was an experience,' Sherlock replied, licking his ice-cream.

John chuckled. 'If you say so.'

'I still hate snakes.'

'You've got one in the fridge at home.'

Sherlock glared at him. 'They're all right dead. They can't stare at you... all wickedly, and horribly...' A visible shudder ran through him.

John hesitated a moment. 'Does Mycroft know you're scared of snakes?'

Sherlock paused. He couldn't lie. 'No... But don't you dare tell him.'

'Oh, I won't. Not until I need to,' John grinned. It occurred to him then that perhaps their trip to the zoo hadn't been entirely useless after all.