What confuses polyphemus about the last ram?

Polyphemus is confused by the last ram because, unlike the other sheep, it does not follow the usual behavior of grazing and bleating. Instead, it lags behind, and Polyphemus notices that it carries Odysseus hidden underneath its wool. This peculiar behavior raises suspicion for the cyclops, making him question why this particular ram is acting differently from the rest. Ultimately, Polyphemus fails to realize that the ram is aiding Odysseus in his escape.