The Clashing Rocks
In thanks, Phineus informed the Argonauts of a danger just ahead on the route to the Golden Fleece - two rocks called the Symplegades, which crashed together upon any ship passing between them. The king even suggested a mechanism by which one might avoid the effects of these Clashing Rocks. If a bird could be induced to pass between the crags first, causing them to clash together, the Argo could follow quickly behind, passing through safely before they were ready to snap shut again. By means of this device, Jason caused the rocks to spring together prematurely, nipping only the tail feathers of the bird. The Argo was able to pass between them relatively unscathed. Only her very stern was splintered.