How big was the first nuclear bomb, code-named Trinity? Detonated in the desert of New Mexico just three weeks before Hiroshima, it's energy was far beyond any conventional bomb. But how big was it? In this first episode on the physics of explosions we recount how the British physicist G.I. Taylor estimated the energy of the bomb just by looking at the pictures of the explosion. Taylor's method requires very limited mathematical background, while being surprisingly effective. It is a classical introduction to an outlook on Nature revealing the mechanics at play behind motion.