What's the difference between ghosts and ghouls?

This two words have same initials and even the first three letters, "Gho", both refer to a kind of spirits. What's the difference between ghosts and ghouls?

Ghost-A ghost is said to be the apparition of a deceased person, frequently similar in appearance to that person, and usually encountered in places he or she frequented, or in association with the person's former belongings. The word "ghost" may also refer to the spirit or soul of a deceased person, or to any spirit or demon. Ghosts are often associated with hauntings, which is, according to the Parapsychological Association, "the more or less regular occurrence of paranormal phenomena associated with a particular locality (especially a building) and usually attributed to the activities of a discarnate entity; the phenomena may include apparitions, poltergeist disturbances, cold drafts, sounds of footsteps and voices, and various odours."

A ghoul is a monster from ancient Arabian folklore that dwells in burial grounds and other uninhabited places. The English word comes from the Arabic name for the creature: ghūl, which literally means "demon". The ghul is a devilish type of jinn believed to be sired by Iblis.

Ghoul- Ghul is also the name for a desert-dwelling, shapeshifting demon that can assume the guise of an animal, especially a hyena. It lures unwary travellers into the desert wastes to slay and devour them. The creature also preys on young children, robs graves, and eats the dead. Because of the latter habit, the word ghoul is sometimes used to refer to an ordinary human such as a grave robber, or to anyone who delights in the macabre.

I now know how to say "ticks" in English

It's always a trouble to express what you know in another language. Cow ticks, for instance, I am so familiar with this parasite, when I started herd my buffalo as early as I was seven. I pressed my face on the buffalo's large stomach while it was grazing on the grass. I was so fond of doing this that a tick went into my ear, and died there. several weeks later, I felt uncomfortable in my ear and went to barber, he dropped some vegetable oil into my ear and picked it out using an ear picker.

But I never know how to say in Mandarin, that is different with my mother tongue which is also a Chinese dialect. When I moved to England, this creature always sneaks through my thought, keeps me wondering how to say it in English.

To day I went to shopping, read a leaflet from Sainsbury's Pharmacy counter, which tells you how to treat pet lice,flea and ticks. Wow!

Google Gear: Offline access is unavailable

I installed Google Gear for offline access to Google Docs, but I got an error message:

There was an error loading data from Google Gears. (Error 3)
Offline access
is unavailable. Please keep your browser open and go back online before
continuing to edit. If this problem persists, you may need to uninstall and
reinstall Google Gears.

I didn't reinstall, and don't know what's wrong with it. While ticks "Work offline", no error message shows up.

If you are reading this post, and found out the cause, please leave a comment here.