When Willie is chasing Diefenbaker toward the lab (lamenting "Fraser's gonna kill me!"), the cameraman's shadow falls across his back.
The street signs point to I-94 North. Although I-94 geographically runs North-South around Chicago, because it is an even numbered Interstate, directions on I-94 are always given as East-West, the geographically northbound lanes around Chicago would be I-94 West.
The street sign shows an intersection of I-94 and IL-161, but I-94 is in northern Illinois and IL-161 is only in southern Illinois, nowhere near Waukegan. The two roads never intersect.
There is a touching scene where Diefenbaker and his mate begin to communicate by barking while in a kennel. Diefenbaker is deaf.