at times , especially of a morning , the jungle din could smother almost any human noisethe screeching of birds , the chattering of monkeys , the rustle of deer and wild pigs as they made their own paths through the undergrowth , the buzzing of flies and mosquitos , the sighing of wind high in the treesit was a constant river of sound that , if you were unaccustomed to it , would swallow footsteps and even quiet voices .