Sentence:  From the east to the west coast of the Korean peninsula was a strip of land in which fear filled men were at that same moment furtively crawling through the night , sitting in sweaty anticipation of any movement or sound , or shouting amidst confused rifle flashes and <WSD>muzzle</WSD> blasts . 
Meaning of the word marked with <WSD> tags:  the open circular discharging end of a gun