Ohalot 9:9 is part of a perek dealing with a caveret (כורת, a beehive-shape thing) with a piece of a dead body (which is tamei) in various positions, and whether the surrounding house is tamei or tahor.
The mishna reads, in part:
היתה ממלאה את כל הבית ואין בינה לבין הקורות פותח טפח, טמאה בתוכה, הבית טמא.
If it [the caveret] was filling the whole house and there was less than a hand-breadth between it and the beams, if there is impurity inside it, the house is impure.
The question is, if the hive reaches to the roof, how does the (piece of a) body get inside, practically speaking? If it had been inside before the hive was brought in, presumably an ohel would have been made during the transfer, and everything would already be tamei.
An answer of "it doesn't -- the case is to highlight the laws, not be practical" is also acceptable.
(This is my brother's question -- he is learning this, not me. I thought it was interesting, so i did a bit of research and posted it. Apologies if i misrepresented any concepts here, as it's been a while since i personally learned this stuff.)