Answer the questions briefly:

To what does the author compare the humming of insects in the bedroom? Why?

The author Robert Lynd compares the humming of insects in the bedroom to the buzz of a dentist’s drill or the saw mill.

The comparison is made to show the scale of irritation that the buzzing of an insect can cause when one is relaxing in his bedroom. Just like the sound of a dentist’s drill or the shrieking of a saw mill is not at all pleasant to hear, much in the same way an insect buzzing in the ear while one is resting in his bedroom can be very annoying and unpleasant.