The number of spirits floating on a Life-Force Door tell how many enemies must be defeated in order to open it. They appear in Star Fox Adventures. A Life-force door looks like a red force field with white waves moving from the edges of the field towards the center. At the center, there is a small horned dinosaur skull and crossbones. The red spirits are very vague and move clockwise around the center. They disappear when enemies are defeated. Once required number of enemies are destroyed, the Life-Force Door starts diminishing from the edges towards the center, finally disappearing from sight and revealing the way behind it.