Sentence:  With the first reports , Russell 's horse wheeled to the right and ran towards the buildings while Cook , followed by a hail of bullets , raced towards the arroyo of Salyer 's Canyon immediately in front of him , just reaching it as his <WSD>horse</WSD> fell . 
Meaning of the word marked with <WSD> tags:  solid-hoofed herbivorous quadruped domesticated since prehistoric times