The first time Sam's anti-possession tattoo was shown, it was an inverted pentagram with one point facing down and two points facing up. When Sam shows his tattoo to the book publisher it is a regular pentagram, with one point up and two points down.
A village would never have one way out (unless maybe it was on an island). There would always be ways in or out just in case of emergencies like an out bridge.
When Dean parks the Impala and checks to see that it is locked as he walks around the back of the car you can see the trunk lid is ajar.
When the boys check into the sleazy motel, Dean tells Sam "the book says I spend the day driving around in the Impala, so I'm gonna go park her". The car is already parked in a parking spot outside their door, he didn't need to go park it somewhere else, and the fact that he did is what caused the stuff in the book to happen to is car.
Sera makes a stabbing motion when referring to how Sam had to kill Madison. In truth, Sam shot Madison.
When asked what Dean's favorite song is he says "It's a tie, between Zep's Ramblin' On and Travellin' Riverside Blues." The Led Zeppelin song is actually called Ramble On, not Ramblin' On.