There is also the belief is that some spirits may have control over other spirits. In some cases, paranormal investigators believe that a gentle spirit is trying to make communication in order to warn people about a particular evil spirit who may have control over a specific location. Or that a good spirit is even staying around to keep a negative spirit from gaining control.
In order for one spirit to recognize the behavior of another spirit, logic would suggest that there is some form of interaction going on between the spirits or ghosts.
If you’re of the belief that ghosts and spirits are beings residing in another dimension that we can’t see, then it may also be possible that these beings are interacting with each other just the same as we are within our own dimension.