As noted in the comments the method for getting a right side up head in an upside down jar is a little tricky but neat (if you want to try it here is the method)
1. you will need a glass jar, a head, a 2x2 round plate and a T-piece.
2. place the t-piece through the 2x2 round plate so that the bar points in the same direction as the studs.
3. place the head onto the t-piece so it inserts into the hole on the top of the head
4. place the jar over the head so it sits over the four studs on the 2x2 piece
5. turn the whole thing over so the head is the right way up.
I used a T-piece but any part with a rod will work, such as a stick 0 3.2 w holder (robot hand) or light sword blade but it must be long enough to give clearance above the studs or the head will not fit on.
Quoting Farhan Salman
Now, how did you done this. Never mind. Awesome spider thingy. Oh, and I watch you're other creation in LEGO.com all of them is awesome.
for this one I got a little more creative. The t-bar piece is inserted through the cross hole in a circular 2x2 plate, then put the skull on the end of the t-bar and put the jar over the top.
I'll add some pictures when I have time explaining it.