Docu on extract():

    Description 
       Import variables from an array into the current symbol table.
       If flags is not specified, it is assumed to be EXTR_OVERWRITE.

       EXTR_OVERWRITE
          If there is a collision, overwrite the existing variable.

The danger is that any state variables set before the extract($_...)'s can be overwritten arbitrarily. This also makes it essential that any and every variable is instantiated prior to any use.