I want to know since I won't read the Divina Commedia in a close future. 
Inferno, Canto XXXIII:
...
And, that thou mayest more willingly remove
From off my countenance these glassy tears,
Know that as soon as any soul betrays
As I have done, his body by a demon
Is taken from him, who thereafter rules it,
Until his time has wholly been revolved.
Itself down rushes into such a cistern;
And still perchance above appears the body
Of yonder shade, that winters here behind me.
This thou shouldst know, if thou hast just come down;
It is Ser Branca d' Oria, and many years
Have passed away since he was thus locked up."
"I think," said I to him, "thou dost deceive me;
For Branca d' Oria is not dead as yet,
And eats, and drinks, and sleeps, and puts on clothes."
"In moat above," said he, "of Malebranche,
There where is boiling the tenacious pitch,
As yet had Michel Zanche not arrived,
When this one left a devil in his stead
In his own body and one near of kin,
Who made together with him the betrayal.
But hitherward stretch out thy hand forthwith,
Open mine eyes;"--and open them I did not,
And to be rude to him was courtesy.
Ah, Genoese! ye men at variance
With every virtue, full of every vice
Wherefore are ye not scattered from the world?
For with the vilest spirit of Romagna
I found of you one such, who for his deeds
In soul already in Cocytus bathes,
And still above in body seems alive!This is an older translation--not as fluid or beautiful as the Hollander translation.
The gist of it is, is that for those who betray guests (as d' Oria did) the soul is immediately taken down to Hell while their (empty) bodies stay above on earth... eating, walking until the body decays and dies (a second time). If that's not a description of a zombie, I don't know what is. 
