A historian's blog devoted to Shakespeare's characters
The person narrating has committed a murder and shoved the corpse under his floorboards. As some time passes the heart beat is a glimpse into his insanity, and how he is delusional over hearing non existent sounds. He believes he hears the heart of the person he murdered under the floorboards, which is a delusion, most likely made out of paranoia. When the police come to ask about the victim, the man almost fools them until he breaks down and confesses. He expressed annoyance at the victim earlier, saying that he could not get away from their eye, I believe. He tried to solve this by killing them, but his mind would not let him do so by making up false realities.
The movie begins on what has already happened...
The mode stands for the number in a series found the most.
In this series you have:
three 4s
two 17s
one 27
one 29
one 20
one 24
and one 34
The mode, or number most found, is 4.