rillet

After that brief moment of frenzy, the viper slithered loose of its own tangles and flowed swiftly across the squashed-shag carpet, as if it were a quickness of water following the course of a rillet.

First, a pearly white, unrelieved, then a trace of faint darkness here and there, and finally, the fine neatly printed equations in black, with an occasional red hairline that wavered through the darker forest like a staggering rillet.