The celebrated KAM Theory says that if one makes a small perturbation of a non-degenerate completely integrable system, we still have a huge measure of invariant tori with quasi-periodic dynamics in the perturbed system. These invariant tori are known as KAM tori. What happens between KAM tori draws lots of attention. In this talk I will present a Lagrangian perturbation of the geodesic flow on a flat 3-torus. The perturbation is C^m small (m can be arbitrarily large) but the flow has a positive measure of trajectories with positive Lyapunov exponent. The measure of this set is of course extremely small. Still, the flow has positive metric entropy. From this result we get positive metric entropy between some KAM tori.