There appears to be some disagreement over what function yes and no perform in the following sentences: Yes, you are right. No, you are mistaken. According to ODO (yes, no), they are being used as ...
As a spin-off from this comment: If a human exclaims something like "ouch!", I believe it's considered an interjection. But if a pig exclaims "oink!", what is the part of speech? And if a bell goes ...