because they serve the purpose of determining the special object of each sense, such as smell and so on.
(they; serve; the purpose of determining the special object of each sense) Context(they serve,List([8, 18))):(they; serve of determining; the special object of each sense)
they serve,List([8, 18))
they they
serve serve of determining
the purpose of determining the special object of each sense
the special object of each sense