That's one way to identify them, but it would be more accurate to say that foreigners are people brought here by--supposedly--the coral, from their own realities.

At the moment this curse seems to involve multiple individuals becoming temporarily attached at the site of contact if they in any way touch each other, but whether or not the curse actually takes effect for any given instance of contact seems to be random, or at least inconsistent. A recent curse involved visible manifestations of someone's fears. Another turned some of the foreigners into animals, and they've done such things as altered a victim's personality or projected their thoughts visually. All recorded cases of curses so far have been inherently harmless, just inconvenient. To say the least.