>>936349299the Resistance uses dogs to detect infiltrator Terminators, like the T-800, which have living human tissue over their endoskeletons, making them nearly indistinguishable from humans visually. Dogs can sense something unnatural about Terminators, possibly due to subtle differences in scent or behavior, and bark to alert humans. This is shown in a future war flashback where dogs at a Resistance bunker entrance detect an infiltrating Terminator, triggering an alarm.