A sorry box is a small and enclosed space used by fluffy horse owners to punish or discipline them for bad behavior. In practice, a sorry box can come in several forms as specific as pet carriers to as improvised as closets, basements, wardrobes, or any space that has some combination of being physically confining or poorly lit, if not outright dark. The sorry box confinement method is preferred by owners who don't want to physically harm their fluffies, with for example a sorry stick, but sometimes, both sorts of punishments are combined.
By nature, fluffies tend to be claustrophobic (afraid of confined spaces) and achluophobic (afraid of dark areas). The trauma of exposure any combination of the two is linearly proportional to duration and is an effective passive means of behavioral correction.
An unfortunate side effect of the sorry box is that it makes the safe transportation of fluffies difficult for everyone involved. Associating a pet carrier as a sorry box, fluffies can sometimes panic with just the mention of being put in a sorry box. Once actually place inside, the fear continues to grow and manifest in cries, screams, pleading, attempts to escape to howling, thrashing, and uncontrollable defecation and urination. In pregnant mares, it has also been linked to miscarriages and stillbirths.
Sometimes, the combining cries to be released with the growing stench of urine and feces in enclosed passenger cars has distracted drivers enough to loose control as to cause single and multiple car collisions on highway and city streets.