"It was so unexpected to get it," says Mr Simmons, proudly showing off a display case in which six dead rats, their tails knotted together in an irrevocable tangle, swim about in formaldehyde like something from the less likely recesses of Damien Hirst's imagination. "What's so brilliant about this is that rat kings are very rare in nature, it is even more unlikely that someone would preserve one and practically impossible that I would get my hands on it when they had. But this one [which dates from 1907] comes from a German museum, who were happy to loan it. I love rat kings because they are incontrovertibly real and totally unexplained."
And thus they fulfill exactly the requirements of an exhibition called "Of Monsters And Legends", a collection of bizarre ephemera that Mr Simmons has put together over the past three years. Presently on display in the strangely appropriate surroundings of Croydon library, it also includes a unicorn horn, a mermaid skeleton, several fairy coffins, a furry trout, objects a malevolent poltergeist threw about a sitting room in Enfield in the Sixties, and the pickled remains of the Stronsay sea monster.
Either that or it is a collection of rather artfully constructed fakes, depending on your level of scepticism.
"What we have here are objects which have been presented as material evidence of strange phenomena," says Mr Simmons. "It's up to you to decide if they convince you."
For instance, there is the toad-in-a-hole that Mr Simmons tracked down in a museum in Brighton. This is a mummified toad that was apparently found in a toad-shaped cavity in the middle of a large piece of flint when it was cracked open.
"The phenomenon has been often reported," says Mr Simmons. "But this one was handed to the museum by Charles Dawson, the prime suspect behind the Piltdown Man fraud. So you may decide it is not entirely kosher."
Dodging the unlikely combination of Uri Geller and Terry Christian, recording an item about the exhibition for a television programme, Mr Simmons leads on into a room that includes a series of photographs of people suffering from bleeding stigmata.
"This one," he says, pointing at a picture of a Russian nun lying in a hospital bed bleeding from wounds shaped like crosses on every extremity, "is the Tarantino of stigmatics."
Indeed, as he talks with unswerving animation about odd things and the manner in which people are so willing to believe in them, it soon becomes clear that the exhibition is something of a culmination of Ian Simmons's life's work. By day he runs In-Spire, a hands-on scientific museum in Norwich. But in his spare time he is a committed Fortean, keen on the ideas propagated by Charles Fort, the 19th-century writer on things unexplained.
"There was never really any doubt that I wouldn't be intrigued by strange phenomena," he says. "My father was caught up in a rain of fish in India during the war. And my mother once encountered ball lightning in Beddington. I suppose you could say it was in the family." Thus when asked by the Fortean Times magazine to curate the exhibition, he jumped at it and spent three years scouring the world for odd bits and pieces.
"I picked up all sorts, but the thing I'm most disappointed I missed was the Minnesota Iceman," he says. This is a huge hairy "bigfoot" in ice, or, rather, it's a rubber replica of the same. The man who owns it claims he keeps the original out of sight for security reasons and only displays a copy. "I flew to Minneapolis to negotiate with him, but it wouldn't fit in to his schedule. A real shame. I'd have loved to have got him."
As Mr Simmons shows off pieces from the Roswell UFO crash ("fragments of alien craft or strips of kitchen foil: you decide") a member of Terry Christian's film crew approaches with a tricky question.
"Where exactly is the bigfoot turd?" Mr Simmons leads them to an alleged remnant of the yeti-like creature from America.
"You've heard of the expression 'weird shit happens'?" he says, holding up a jar filled with small pieces of black excrement. "Well, this is the weird shit itself." Then, peering closely at the jar, he adds: "Actually, it looks more like owl pellets to me."
'Of Monsters and Miracles' is at Croydon library until 19 November.