Expensive labs and equipment are out, so Gupta’s syllabus demands only ‘Ten Little Fingers’, retrieved rubbish and the free spirit of discovery to learn about complex scientific concepts. A national award-winner for science popularisation among children, particularly among the poor and underprivileged, Gupta’s classes are often held in the outdoors. And he needs only matchboxes, broomsticks and slippers to explain everyday phenomena like light and its daunting laws of convergence and divergence. Taking an old rubber sole (he says Bata’s hawai slippers are the best) planted with three old ballpens, the kids merely bend the sole forward till the pens touch each other, like rays of light in focus, and then bend it backwards until the pens split into separate rays to demonstrate divergence. "It is nothing but hocus-pocus," he says, but for most kids the ‘slipper-flipper’ is a simple, fun experiment whose results are unforgettable.