There are situations where my fulfillment of an obligation depends on there being no interruption between the bracha and the action it covers (like between washing and making motzi) and there are situations where my fulfillment requires that there be no interruption of the one performing the action and my listening (though that is a clunky wording), like the reading/hearing of the megillah.
But why would an interruption change the mindset (his kavannah to make me yotzei and my kavannah to be made yotzei)? If I sneeze, is that an interruption which should make me not exempted? Is my saying baruch hu uvaruch shemo (which is a manifestation of my focus on the words of the bracha) a heisach hada'at if I still hear everything and am listening to the words? Is making noise when the koreh says "Haman" any more or less of an interruption if I still hear all the words?
