Culling the Herd is a pet talent located in the 3rd tier of all the pet talent trees. It increases hunter's and pet's damage dealt, each time Claw, Bite or Smack critically hit. This pet talent was introduced in Patch 3.3.0 to replace Avoidance, which was given as a passive treat to all non-Death Knights' pets.
Patch 3.3.0 (08-Dec-2009): This pet talent has replaced the Avoidance talent in the pet trees (Hunter pets now gain that benefit automatically without expenditure of talent points). Culling the Herd increases pet and hunter damage by 1/2/3% for 10 seconds each time the pet deals a critical strike with Claw, Bite, or Smack.