| MadSci Network: Physics | 
Hi Adela!
This is thought to be caused by electric discharge; a bunch of tiny sparks.
Whenever tape is peeled from a surface, both the surface and the
tape's adhesive become strongly charged.  I have an article on my
website about this:
Sticky ElectrostaticsHere's an article about this:
http://www.amasci.com/emotor/sticky.html
"In the peel zone: Tape's electric gooeyness," 
by I. Peterson, SCIENCE NEWS, 
Vol 146, p277 Oct. 29, 1994
Try the links in the MadSci Library for more information on Physics.