Monday Puzzle

The Presurfer, in cooperation with pzzlr.com, brings you a puzzle every Monday. Just to tickle your brain.
image credit: James Michael DuPont cc
Having a practice run for Halloween, three little ghosts are going along in single file. The first ghost says 'There's a ghost behind me.' The second ghost says 'There's also a ghost behind me.' And the third ghost says 'Yep, there's a ghost behind me, too.' How is this possible?
You can find the answer here.