We are contemplating a urinal. Not just any old urinal, but Marcel Duchamp's 1917 urinal, which he turned upside-down and labelled "art".
I should make it clear from the outset that this is not my field. Or fields. I am qualified to teach neither art nor plumbing. But that's the way it goes in further education. The longer you teach, the more you find yourself wandering into unknown territory - faraway countries of which you know little.
On the timetable it says that what we are actually engaged in on this gloomy Monday morning is study skills. And what I am trying to demonstrate to my class of slightly bemused adults are ways in which they might improve their essay writing.
The image of the urinal that's on the whiteboard, there in all its upside- down incongruity, is an essential part of this. I have given the class a research-based essay, written by a former student, for them to analyse.
As the essay is on the early 20th-century avant-garde art movement known as Dada - his choice - I realise that some background is called for.
Dada, I tell them with all the authority of the total amateur, was essentially an anti-art movement; a reaction against art as a "commodity", art that could be bought and sold in a market.
I explain that when Duchamp created the urinal, he gave it the title Fountain and signed it not in his own name but that of R Mutt. The artist was, according to his latest Wikipedia entry, "a playful man".
"Was he taking the piss or what?" comes the inevitable question.
"Well in a way he was," I reply, searching for a modern parallel. "Think of it like punk music - a violent attack upon the establishment, on the cosy way that popular music was going at the time."
This analogy is only a partial success. One or two reluctantly concede that they have heard of punk, or read about it in history books. One or two more admit the same about "popular music".
"What about modern-day conceptual artists?" someone asks. "You know, Damien Hirst and his shark?"
"Great," I say. "Someone's got their brain in gear." Others rush to follow up on this lead.
Pretty soon we are in Tracey Emin's bed. As she also produced a work entitled Everyone I Have Ever Slept With, involving more than 100 names sewn into a tent, we are not short of company.
Inevitably, we find ourselves discussing the wider topic of modern art in general, its worth and validity. The consensus is one of intrigued scepticism.
Emboldened, I embark on one final contemporary parallel. There is, I remind them, an ongoing controversy around the Tate Modern's latest work of conceptual art: Doris Salcedo's 548ft-long crack, which runs the entire length of the floor of the gallery's Turbine Hall.
Several of them know of it. One has even visited the gallery to have a look. Most, though, are clearly having problems getting their heads around the concept. "You mean, it's like, like . a crack? In the floor?" asks one.
"Yes," I say. "But it's a very carefully designed one."
"What's the point?" asks another.
"According to the blurb at the gallery," I explain, "the crack is a vital metaphor for the state of our world today."
"How long till lunch?" comes one student's response.
As lunch is still 10 minutes off, I decide to tell them about my own visits to the exhibit. Unimpressed by my first viewing, I went back to try to get a different perspective. I had been told that if you look down from the mezzanine floor above the Turbine Hall, the overview is impressive. I duly observed from above, but in truth felt it added little to the experience.
Then I spotted a much smaller crack in the mezzanine floor itself. I accosted a passing attendant. "Is that part of the exhibit?" I asked."Don't be so silly," she said, with not a little scorn. "That's just a crack in the floor."