View Larger Version | Frog embryos know when to cut and run. As a cat-eyed snake bites into fertilized eggs of a red-eyed tree frog in Costa Rica (left), embryos that don’t go down the snake’s throat early in the attack escape by hatching and dropping off the leaf. In tests of hatching cues, researchers mimicked vibrations from a parrot snake attack (below, top) and a rainstorm (below, bottom). Embryos fled from the simulated snake but not from the storm, apparently assessing risk based on a combination of the duration, frequency and spacing of shake-ups. Credit: K. Warkentin/Boston Univ. and Smithsonian Tropical Research Institute