New Delhi, May 21 -- Convulsing bond markets mean different things to different people. If you run a government, it is plainly bad that government-borrowing costs are shooting up-as they are across the world. The yield on Japan's 30-year debt has shot above 4%, its highest ever; America's has topped 5%; Britain's is chugging fitfully towards 6%. Since mortgage rates tend to move in line with these yields, anyone looking for a new one will also feel the pinch. For bond traders, in contrast, the past few weeks have been quite the thrill. A decade ago near-zero interest rates seemed to have permanently shoved their market into the deep freeze. Now it is red hot.

It is not hard to see why. Inflation and yawning government deficits have worri...