Her dark form came within the inverted cone of water-light wherein movement above was visible to a trout waving fins and tail behind a sunken bough. While the otter was swimming down to the rocky bed, she saw the glint of scales as the fish sped in zigzag course to its cave. The otter was six feet under the surface, and at this depth her eyes, set level with the short fur of the head, could detect any movement above her in the water lit by star-rays. She could see about four times her own length in front, but beyond all was obscure, for the surface reflected the dark bed of the river. Swimming above the weeds of the pool, she followed the way of the trout, searching every big boulder. She was way-wise in the salmon pool. In underwater pursuit her acute sense of smell was useless, for she could not breathe. She peered around the rocks, and in every cave in the bank. She swam without haste, in a slow and easy motion, with kicks of her thick webbed hindfeet, and strokes of her tail which she used as a rudder to swing herself up or down or sideways. She found the fish under an ash-tree root, and as it tried to dart away over her head, she threw herself sideways and backwards and seized it in her teeth. By a bay in the bank, broken and beaten by the hooves of cattle going to drink, she ate her prey, holding it in her forepaws and cranching with her head on one side. She ate to the tail, which was left on a wad of drying mud cast from a hoof; and she was drinking a draught of water when a whistling cry came from under Canal Bridge. It had a thin, hard, musical quality, and carried far down the river. She answered gladly, for it was the call of the dog-otter with whom she had mated nearly nine weeks before. He had followed her down from the weir by the scent lying in her seals, or footprints, left on many scours, and on the otterpath across the meadowland of the river's bend. He swam in the deep water, hidden except for his nose, which pushed a ream on the surface placid in the windless night. As she watched, the ream became a swirl. The otter on land heard the instant hiss of breath in the nostrils before they sank. Immediately she slipped into the river with the least ripple tracing where she had entered. The dog-otter had sniffed the scent of a fish. Bubbles began to rise in the pool, making two chains with silver-pointed links, which moved steadily upstream. Twenty yards above the swirl, which lingered as the sway of constellations between black branches, a flat wide head fierce with whiskers looked up and went under again, the top of a back following in the down-going curve so smooth that the bubbles rising after it were just rocked. Time of breathing-in was less than half a second.