In the sexual universe, all sorts of things can feel good, even if we humans have a hard time imagining how they can bring any pleasure. Electricity, for example, may be nothing for us beyond a painful shock. But for some fishes, it is the essence of desire.

The rivers and lakes of central Africa are home to a couple hundred species of fishes called mormyrids. Their tails are packed with special cells that can produce electric discharges, and they use other kinds of cells embedded in their skin to detect the field they produce. If another fish passes by them, the field becomes deformed, and the mormyrid can sense the difference.

What must it be like to be able to sense