Okay, here it goes... 

There is this one building, which is very tall...
The other, is very small...
I'm gonna give you a while to see the difference.
Oh, yes, and its NOT the height... 
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Give up?

Okay, the answer is... When a person falls from :

The tall building : They shout, "AAAAAAHHHHHH!!!" *wham!*

The small building : *wham!* "AHHHHHHHHH!!!"

Heeheehee... get it?