A large hoofed mammal having a short coat, a long mane, and a long tail, domesticated since ancient times and used for riding and for drawing or carrying loads.
Using either one or two hands is acceptable. Both hands are used in the context of formal register (e.g. teaching ASL in class or storytelling for children). Casually use one hand.
Trivial tidbit: A horse can look forward with one eye and, at the same time, look back with the other eye.
Gloss: gate open[t], ix black horse cl-run cl-gate/cl-horse-path
English equivalent: The black horse ran through the open gate.
In the last part of the sentence, the referent of the gate is a classifier while the other referent of the horse is a classifier making a path movement (classifier predicate).