At the beginning of the film, Milo is seen as a very young kitten, perhaps three weeks old, nursing from his mother. When Otis the puppy scrambles up to their nest in the barn, a curious Milo topples over the side of the nest and the two animals meet for the first time. Strangely, from the moment he topples out of the nest to the moment when he lands next to Otis, Milo has aged at least a month!
A young, small and scrawny raccoon waits on the riverbank for Milo to catch a fish with his tail. When Milo catches the fish and drags it ashore, the raccoon is suddenly a full-sized adult, clearly twice the size of the raccoon in the previous shot.
When Milo is a kitten and a young adult his eyes are yellow, but when Milo becomes a bit older his eyes change to green, and then the eyes are back to yellow again. This is before the Milo ends up in the box on the river.
When Milo's kittens are born, there is one calico kitten that is clearly seen while they are indoors. When the cat family goes outside to meet Otis' family, all the kittens are orange and white, like a mixture of Milo and Joyce would actually be.