Sentence:  With the first <WSD>reports</WSD> , 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 horse fell . 
Meaning of the word marked with <WSD> tags:  a sharp explosive sound (especially the sound of a gun firing)