They're capable of altering our memories, and even personalities and how we behave. In the past there have been attacks, too. Both by creatures which normally are confined to Sector Six, however also there was a time where a creature who fed on fear was roaming around.
[Just to start with.]
In a general sense, the flow of time is different. For example, two people could be here from the same world, but one could be from a point in time that was the past for the other person.