How to spot a ghost?

You know my love and my fascination for All About Ghosts, the book of paranormal that fired up my imagination when I was a child. And made me a very superstitious and gullible child as well. But if I ever write horror stories, this book will be one of my main sources of inspiration. It also has lots of useful tips, such as how to spot a ghost, as you can see above. The last two points are rather obvious, but the first two are rather interesting, for whoever keeps in mind that ghosts are not only wearing white sheets.