Banquo's spirit animal is a dog because he is very loyal to Macbeth. No matter how much wrong Macbeth did, he stuck right by his side. Even when Macbeth asked, Banquo said without hesitation that he would continue to be loyal. Banquo is also calm and collected, much like older, well trained dogs. He does what Macbeth says and never questions it. When the witches told them their prophecy, Macbeth was thinking of everything he needed to do to fulfill that, whereas Banquo was go with the flow, calm and collected.