We study the contour (or contact) line of a large water puddle floating on an organic liquid substrate. The line tension Tis a two-dimensional analogue of surface tension. We manipulate the line through a vertical metallic rod. (i) When stretched by a horizontal force f, the line makes a kink characterized by an angle 2theta (f = 2T-cos theta), which allows us to measure T. (ii) Moved sinusoidally, we generate "triplons" of wavevectors q along the line. In the gravity regime (qkappa(-1) < 1, where kappa(-1) is the capillary length), the measured dispersion relation is omega(q) similar or equal to q(1.51+/-0.05). An improved version of our previous dynamical model gives an exponent 3/2.