Here are a few possibilities for why someone might ask this:
* A riddle: This could be a riddle where the answer relies on wordplay. For example, the answer might be "a teapot," as it has a spout that could be considered a third "ear".
* A fantasy creature: In fantasy stories, there are often creatures with unusual features. A three-eared creature might be a fictional invention.
* A mistake: Perhaps someone is simply mistaken about the number of ears an animal has.
Do you have any more context for this question?