While in the magic jar, the character can sense and attack any life force within 10 feet per caster level (on the same plane). The character does need line of effect from the jar to the creatures. The character, however, cannot determine the exact creature types or positions of these creatures. In a group of life forces, the character can sense a difference of four or more HD and can determine whether a life force is positive or negative energy. (Undead creatures are powered by negative energy. Only sentient undead creatures have, or are, souls.)