Bava Kamma 17 - Innocent and Established Damagers

What difference exists between the nature of the half payment in the case of an innocent and the nature of the full payment in the case of an established damager? The owner's liability in the case of innocent first-time gorings is limited to the value of the ox that did the damage, and in the case of established damagers the owner pays pays the full amount of the damage with his best property.

Regarding what is the foot of an animal considered an established damager? For breaking things in the course of its walking but not when kicking.