Gecko mania.

Snap, and the tape is loaded. A final adjustment of black curtains: the camouflage that allows us to a window on this now-familiar world. We're spies at the ready, an uninterrupted hour of geckp-tracking ahead of us. Light out, and a deep silence descends, punctuated only by the occasional splash of turtles in the room next door.

This is Tank Room C8C by night. It's got four precious inhabitants. From the outside, no-one would guess that here heirachies are fought out, predator-prey struggles are won and lost, and pregnant tummies are expanding to bursting point. By night, as I stare down the barrel of a camera at this tiny world before me, it seems so stable. To watch minature lives being played out is somehow reassuring.

Julia and I have been so busy gecko filming lately that we have been (admittedly fairly appropriately) dubbed Team Geeko. We've been struggling with the problems posed by filming small things in the dark: infra-red light and if there's enough of it, backgrounds and how to hide them, shallow depths of field and how to work with them. After weeks of long nocturnal hours filming in the dark dampness of Tank Room C8C, squinting at a screen the size of a matchbox, these secret lives may be magic, but the fairy dust is wearing a little thin.

And yet, when we're in there and they're up to something, we're spellbound. We're outraged by the butch one and her bullying nature. Who gives her a right?! We pity the victim and wish that the shy one would come to trust us. Even their attempts at escape fascinate. If they're up to something, the hour zips by - we're viewers in a trance.

But then that camera barrel flashes and the spell is broken. Lights on, geckos into hiding. Tape changing time. That stable world suddenly seems so tenuous. It's a box in a room in the middle of a city. And we're in charge. It terrifies me.