When the person touches a doorknob, suddenly, the extra electrons that have built up are discharged -- flow away -- causing a tiny spark and a small electric shock.
(the person; touches; a doorknob) (the extra electrons; have built up; ) (the extra electrons that have built up; are discharged away; T:When the person touches a doorknob; T:suddenly)
the person the extra electrons the extra electrons that have built up
touches have built up are discharged away
a doorknob
T:When the person touches a doorknob T:suddenly