Silver, Salt, Holy Water Test

As many supernatural creatures. demons and ghosts are vulnerable to silver, salt and/or Holy Water, these substances are used as a test by Hunters to help determine whether someone is human. It is not foolproof - for example it failed to detect that the Adam Milligan was in fact a ghoul disguised as the real Adam.

Episodes

4.01 Lazarus Rising

When Bobby finds a resurrected Dean on his doorstep, he assumes it is a supernatural being and tries to kill him. Dean tries to prove his identity by cutting himself with a silver knife, and they embrace. Bobby then checks whether Dean is possessed by dousing him in holy water.

4.19 Jump The Shark

When Sam and Dean meet Adam who claims to be John Winchester's son, Dean tests Adam with silver and holy water. He doesn't react to them, however he is not human, he is a ghoul.

5.04 The End

When Dean is captured by Future Dean in the year 2014, Future Dean tests Past Dean with Silver, Salt and Holy Water.

7.17 The Born-Again Identity

When the hunter/taxidermist Mackey meets Emmanuel, he does the ritual on Emmanuel and tells Dean that he's the real deal.