When Castiel has the demon knife hidden behind his back, the blade is a shiny chrome instead of the usual flat metal tone.
Whenever Dean used the electrified "joy buzzer" ring he was also a part of the circuit and should have also burned up.
When Sam and Dean figure out that all the strange phenomena are happening within a two-mile radius, Dean asks "Our motel isn't in that circle by any chance?" Sam replies "Yeah, why?" as if nothing odd has happened in the hotel room. But they already tested the buzzer on the ham in their motel room, which cooked, so Sam shouldn't be surprised that the motel is within the circle.