During autumn, large herds of migrating symets pick their way among the low hills and fill the air with their chorus of pings. When herds find water sources in desert areas, such as wide rivers, they rush in to drink. A huge cloud of dust will hang over and behind a herd, lingering in the air for miles.
When predators, such as skewers and Eosapiens, attack, they immediately hear targeting pings and instantly become aware. The herd members, however, waste no time in useless panic. En masse, the entire herd starts to trill in an effort to jam the hunters' sonar. However, skewers can often be undaunted by this.These herbivores are curious animals that appear to have a head at either end of their trunk, and as predators charge toward them, they begin to turn in place, rotating rapidly in a gathering cloud of dust. They stop and it is revealed why nature has equipped these animals with a head and tail of almost the exact shape and size: it is hard to tell which end of the beast is which. To a creature relying on sonar recognition, they present a confusing image. The direction of their imminent pursuit is completely conjectural. This is why they are named symets, for their protective symmetry.
As percentages will have it, symets can leap clear, their would-be killers veering off to regain momentum for a second pass. Sometimes, though, a symet will not be so fortunate and end up getting killed and eaten by a predator.
- In the television special adaptation of the book, the symet anatomy of head-and-tail confusion was incorporated into the litteralope.