The Mishnayos in the beginning of the 4th perek of Eiruvin discuss the halacha if one left the area of his/her techum on Shabbos b'ones (e.g. one is kidnapped and dragged outside the techum) - the person can then only walk 4 amos, unless he/she is in an enclosed area. Later in the perek (mishna 5,) the Mishna discusses a case of one who fell asleep on Erev Shabbos and had no da'as to be koneh shevisa - the Chachamim hold here as well that one can move around only within 4 amos. The Mishna then has a machlokes whether those 4 amos are calculated in each direction, or is it 4 amos total, meaning 2 in each direction. My son Eliezer asked: why does the Mishna wait until 4:5 to discuss the details of how to calculate the area of 4 amos? Why not discuss this earlier in the perek when the din of 4 amos was first mentioned?
I could not find an answer, so his reward for such a kashe is the fame of being mentioned here ; )