When Dexter leaves the cabin to go to the hospital, he is wearing the same clothes. Blood that was clearly on his "kill" sweater is no longer on the shoulders and chest as it was at the cabin.
As meticulous as Dexter is, he would have a change of clothes packed. It would be suspicious if a man were to show up later the same day in a different set of clothes.
The beer Deb and Dexter are drinking during their dinner has no bubbles or foam whatsoever. It is clear water.
When Dexter is with Rita and the kids in the Slice of Life you can hear when the kids throw the hook into the water, however you can still see the bait on the fishing pole without moving.