Natural Rhythm

Transmutation
Level: Druid * 2, Hunter * 2
Components: V, S, M (a handful of pebbles dropped one by one onto the ground)
Casting Time: 1 Standard Action
Range: touch
Target: creature touched
Duration: 1 round/level
Saving Throw: Will negates (harmless)
Spell Resistance: yes (harmless)
  You enhance a creature's ability to harm an opponent based on the number of times it has already injured that opponent with a natural attack. Each time the creature successfully strikes an opponent with a natural attack, the subject gains a cumulative +1 bonus on damage rolls made against that opponent when making natural attacks (maximum +5 bonus). If an attack misses, the bonus to damage for all attacks resets to +0.