Carnivorous plants like the Venus Flytrap hold a gruesome fascination for young brains and little fingers, so it's rare to find one open when kids are around. Most get tickled surreptitiously and snap shut on the non-existent fly. You can almost see the hungry disappointment on the poor plant's face.
"We can't look inside them now," Neil Paterson tells the party of schoolchildren following him around the tropical glasshouse at Dundee Botanic Garden. "So let's look instead at this other insect-eating plant - a pitcher-plant from North America."
He unrolls the long stem to reveal what looks like a cluster of black sultanas. "They're flies, half-digested by the kind of juices we have in our stomach," he says. "I once found three wasps in a row in one of these.
"But this is funny, isn't it? Why do plants, which make their own food, want to eat insects?"
The Forthill Primary pupils look suitably puzzled. "It's because insect- eating plants live in boggy ground," Dr Paterson tells them. "It's hard to get nitrogen out of boggy ground, so they've evolved ways of stealing it from the bodies of insects. In this country we have the sundews that live by the side of Highland streams."
The guided tour takes in all kinds of exotic plants - strangler fig, lipstick plant, Cissus gongylodes - and their strange stories and strategies for catching sunshine in the lush rainforest, before moving through to the dry heat of the desert glasshouse with its tall cacti, gnarled and pitted with age.
Teacher Jacqueline Craig takes a moment to explain why she has brought her P6 pupils to this morning's Dundee Science Festival event. "The rainforest was our topic last term. So we've been doing rainfall charts and things in class to tie in with maths, and writing reports for language.
"It's great for them to see what we talk about or look at in books. I've noticed, as we're walking around, that this is engaging some children who pay less attention in class. They're asking questions and touching plants. You can't get that opportunity in a classroom, and it's nice to get real science from the professionals - for us teachers as well as the pupils."
The rainforest is young Kathryn's favourite topic since P2, she says. "It's so colourful. I like how everything doesn't have to be the same. Like in this country the plants are all dry, but in the rainforest they're wet and if you brought one here it would die. Everything has its own place to live.
"The rainforest is in trouble, though, because people are cutting down the trees to make paper. There are charities that help and we are giving money to them."
Ross has learnt loads this morning, he says. "All about different plants and creatures. I never knew there was a Swiss-cheese plant. It has huge leaves with holes. I didn't know cheddar cheese gets its red colour from the lipstick plant. I like new things.
"I really like the plants that eat insects. It is a bit horrible but that's what things have to do, to live or die."
As the Forthill pupils embark on the second half of the morning's activities - a "Plants for People" search around the whole garden, guided by detailed teachers' notes and worksheets - their place in the glasshouse is taken by a smaller set of pupils, teachers and parents from Glebelands Primary.
"We're a nurture group of children from Primary 4 to 7," explains support for learning teacher Sarah McCowan. "So it's kids who need a bit of social, emotional and behavioural support. This is a new group and we want to do more of this kind of thing.
"It's not just about academic learning. It's getting them out and about, interacting with people and with each other."
As the youngsters follow Dr Paterson around, looking at damp leaves and flowers and listening to his stories, they are lively, well-behaved and interested in everything:
"Are there frogs in your pond?"
"Do you have any palm trees?"
"How come you know so much?"
This is a fun day out of school, young Ali says. "It's a lot better than spelling tests."
Dr Paterson agrees. "I'm education officer at the Botanic Garden, as well as being a chartered accountant. Botanist or accountant, it depends what day of the week you get me.
So which does he prefer? "If you don't mind me saying so, that's a silly question," he replies.
"This is wonderful."
GROWING APPETITE FOR HOSTING SCIENTIFIC DISCOVERIES
Dundee Science Festival's primary programme has grown in recent years from eight schools hosting events to 17, says Tayside manager of Techfest Setpoint and primary programme manager Jennifer Young. "We've also gone from a couple of venues out and about to half a dozen."
Besides the Botanic Garden, these include some of Dundee's most attractive locations - Discovery Point, Mills Observatory, Verdant Works, Templeton Woods and Claypotts Castle.
"That's for medieval construction and it's new this year," she says. "It's about how they managed to build huge castles and cathedrals without any modern equipment. How they solved the problems of moving and raising huge pieces of stone into place. There's a lot of problem-solving and challenges for the pupils. They work in teams and the Historic Scotland people dress up in the costumes of the time.
"I watched the full show yesterday. Kids and teachers were loving it."