  In his seminal paper, Bretherton [J. Fluid Mech., 10:166 (1961)] studied the
motion of long bubbles in capillary tubes, a situation encountered in many
two-phase flow systems. Here, we unveil experimentally and numerically the
negative configuration, wherein a long liquid drop formed by the rupture of a
liquid plug is stably transported in a capillary tube and surrounded by a
flow-induced air cushion. After a careful theoretical and numerical analysis of
the drop formation process, we show that the shape of the drop and lubricating
air film is reminiscent of Bretherthon's calculation and can be inferred from
an adapted analytical theory. This work opens tremendous perspectives for drop
fast transport in microfluidic systems without walls contamination and
friction.
