Entry marks are marks left by a Goa'uld parasite when entering the body of a host. They are typically on the neck, the parasite's preferred method of entry, as this allows easy access to the spinal cord, though any point in the body will work. They also prefer the neck as they do not wish to see the horror on the hosts face when they look in a mirror. The Tok'ra dislike this method, and instead enter through the mouth. (SG1: "Children of the Gods", "Thor's Hammer", "The Tok'ra, Part 2")