When Dean goes into the tomb it is shown to be night. But later through a window behind him you see that it's daytime outside.
At the bar, the amount of foam at the top of Dean's beer continually varies.
Sam and Dean determined that whatever is after Adam is a corporeal creature and not a spirit like a demon or ghost because it is only traveling through small confined spaces like ventilation shafts and sewers, something a spirit would not need to do. Yet when Sam and Adam are setting the trap for this thing in his house they are putting down salt lines, and salt is only known to repel demons and ghosts.