Investigating simultaneous minimum and maximum in CORMEN3.

Confusing from p.214-215:
    .... We compare pairs of elements from the input first with each other, and
    then we compare the samller with the current minimum and the larger to the
    current maximum, at a cost of 3 comparisons for every 2 elements.

    How we set-up initial values for the current minimum and maximum depends on
    whether n is odd or even. If n is odd, we set both the minimum and maximum
    to the value of the first element, and then we process the rest of the
    elements in pairs. If n is even, we perform 1 comparison on the first 2
    elements to determine the initial values of the minimum and maximum, and
    then process the rest of the elements in pairs aa in the case for odd n.

What does it mean by "process in pairs"? Why the different treatment for odd
and even inputs? It seems to work fine in my tests though.