There is nothing more terrifying than the idea of a blood-spatter analyst for the Miami police department actually being a serial killer in his free time, using his knowledge of blood to help catch criminals for the police department and personally doing away with the criminals the police department can’t catch. However, this season of “Dexter” also includes John Lithgow’s naked backside, which may be even scarier than a killer sociopath who walks among us. Maybe we should all feel safe with the idea that there is someone out there making sure that hardened criminals don’t get away with crimes they can’t be convicted for, but it’s more the hardened criminals and the crimes they commit that I find creepy. Whether it’s John Lithgow’s carefully planned murders – he plays the Trinity Killer, a man who always kills in threes, following the same pattern every time – or the mysterious killer of season one who seemed to have it out for Dexter – recreating Dexter’s childhood memories, while including disembodied limbs at the scene of the crime – the killers that roam the streets as innocuous individuals who seem like they would be better suited to grinding coffee beans than grinding bones are the ones I’m most creeped out by. “Dexter” presents a world where you can sympathize with a cold-blooded killer. Michael C. Hall is the gentlemanly blood-spatter analyst who is really quite skilled at his job, and he is a committed boyfriend to his sometimes-needy girlfriend, Rita, played by Julie Benz. Dexter is always dependable, and his sister, Debra Morgan, played by Jennifer Carpenter, often looks to him as source of support and guidance. No one knows of his secret life as a killer, and he takes great pains to keep it that way – there is little guilt about the lies he tells and the furtive nature to his actions, whether it’s lying to his girlfriend about where he goes late at night, or using police department resources to catch criminals. Now in the middle of its fourth season, “Dexter” is back on the upswing after a slightly disappointing third season. Maybe it’s the presence of just one opponent throughout the season, or maybe it’s because Rita is getting a little less screen time, but this season has my heart pounding at the end of almost every episode, and I can’t wait for the following week’s installment. With Halloween coming up, you may be looking for a way to creep yourself out before you head out to any parties, and “Dexter” is a good way to go about giving yourself the heebie-jeebies. Just try not to imagine that the person walking in front of you might be a secret sociopath, or that you might witness the next episode of vigilante justice, and you’ll be fine. “Dexter” airs Sunday nights at 9 p.m. on Showtime – which gives you just enough to time to catch up on this season before the next episode.