How can straw be amusing?

The Grandsprogs were taken to the Eden Project yesterday. They are regular visitors. 
Background.......The lads have been used to using the ladies changing rooms at the pool. The elder is getting embarrassed by having to use Ladies loos if Grandpa isn't around to look after him.............so they have seen a bit! Unfortunately I was unable to accompany them.
At Eden there is a display showing how much our lives depend on bees, butterflies etc. Central to this mosaic are two mannequins, male and female. The boys giggled, as young chaps do, when they saw the mannequins were nude and correct in every detail, except for the female of the species. For some obscure reason her pubic region was covered in straw. Much was the squawking and ruffling of Grandma and Mum's feathers when the elder piped up, "Grandma, that's not right, all ladies have black hair there don't they!" 

Well Grandpa is proud of his boys, roll on the time they discover natural blondes or redheads. I hope I'm around to remind them.