Exactly how does a snake slither across the ground? Scientists long assumed that the reptile pushed against rocks and branches to move forward. But that theory lacks legs, according to a new study. After watching snakes wriggle up rough fabric surfaces or (less successfully) smooth surfaces, scientists from New York University and elsewhere say the secret is in the scales. The belly scales are oriented so that they snag on irregularities. By pushing parts of their belly down to take advantage of this friction, the snakes have enough leverage to speed ahead.