The problem that arises 
here is that since many disfluent words are copies 
of fluent words, if the same cost is used to align 
fluent and disfluent words, the alignment will be 
ambiguous (i.e. there will be multiple alignments with the same cost).
to force the aligner to 
prefer aligning null (i.e. deletions) for disfluent 
words and copy for fluent words, we modify the 
alignment weights so the intuitively correct alignment scores better, and so will be chosen by the 
alignment algorithm