Why is it better to have round manhole covers than square ones?

This is logical rather than lateral, but it is a good puzzle that can be solved by lateral thinking techniques. It is supposedly used by a very well-known software company as an interview question for prospective employees.

Answer to the Puzzle

A square manhole cover can be turned and dropped down the diagonal of the manhole. A round manhole cannot be dropped down the manhole. So for safety and practicality, all manhole covers should be round.

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