When the DNA hairpin is unzipped into single-strand, oligonucleotides complementary to the hairpin sequence are allowed to hybridize.  During the time course of the rezipping process, the bound oligonucleotides cause transient blockages.  The time course measurement of hairpin length allows for the determination of the exact position of the hybridization, as well as the presence of mismatches between the oligonucleotide and the hairpin.