<span>more time than you think you will need because you need to first think and than write. You should always spend more time thinking. </span>
Complete sentence. The comma is used the right way so it wouldnt be a comma splice, and if you replaced the comma with a period it would be wrong, so not a run on. That is why it is a complete sentence
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.
Suppose
Here's a link to help you further
http://writingexplained.org/suppose-vs-supposed-difference
