Everybody stutters or hesitates a little bit at times. It's just that we are hypervigilant in noticing small stutters in ourselves and others, our brains are wired that way. Has something to do with natural high dopamine production, which makes you notice small details Got this from the excellent book 'The Perfect Stutter'. Maybe your colleague is wired similarly and therefore sensitive to it. Most people don't get influenced by our stuttering though.