The creature lying on its back is two feet long. Its plump, segmented legs work furiously to no effect. Its antennae probe an unexpectedly alien environment. Its semi-translucent abdomen appears bloated with what is almost certainly human blood!
Keanu scratches his head in bewilderment. At least I hope it's bewilderment, for he's examining a strand of Lucretia's hair under the digital microscope - which is in turn linked to the projector so I can check he's not on bigboobs.com.
With all eyes now on the screen, I am aware of a voice in my head whispering "Houston, we have pupil engagement".
This is when the old urge comes back and I find myself itching to teach them something. Desperate to seize the day and grab their attention with one cold, calculated statement of fact: "It's called pediculus capitis, and it survives by eating into your scalp and sucking your blood."
I stem the rising tide of revulsion - and the rising tide of Lucretia's tears - with a Peter Cushing stare, and pause to let the shock factor hit home. It's nitpicking I know, but shock factor isn't what it used to be.
Up on the screen, the fat little insect fails to come up to scratch. He's definitely coasting in his efforts to escape. The myth that head lice can leap distances in excess of six feet and swing from hair to hair like miniature Tarzans is cruelly exposed.
I want Terminator, but all I'm getting is Humphrey Bogart as Rick in Casablanca: "Of all the hair fibres on all the heads in all the world she plucks out mine." Keanu's glib announcement that you can zap 'em easy with this special shampoo stuff might have been the final straw, except...
"I'll tell you about those shampoos, shall I? Do you know they contain organo-phosphates which can severely damage the nervous system? Cause hideous birth defects? Blindness? Deformity?" They hang on my every word. I wonder if the Department for Education and Skills might use me in their next recruitment campaign. "Use your head louse, teach."
Steve Eddison is a Year 6 teacher in Sheffield