Without making a big deal about it, but sometime in "passing" you might want to mention it to the sub. Your son *should* receive credit for a correct answer when he can give a reasonable explanation. Menagerie and BillyZ have correct answers b/c they have reasonable explanations. That is why I asked if it was a part of a unit on farm animals or similar b/c then the context would be w/in that unit. Since it was random the teacher should be more flexible in accepting answers.
As for the "close, longer, shorter" assignment. Those things always drove me crazy! Longer/shorter can be measured and have right answers. Close is such a matter of opinion. I would say that the mall to the north of us is fairly close, but my husband will tell you that it is not. Which of us is right?
But the poor sub, she is getting paid significantly less than a regular teacher, even though she is long term. She gets less respect than the teacher will, too. So if you are generally happy with the job she is doing I would just wait to ask her when it is a relaxed time.