Ok,any discussion is welcome.

half a dozen of people should be half a dozen people. è  No, “of “ should not be there.

without too much effort from my side. on my side or from my side? not sure, but definitely on my part.  è I see, you are determined to change my vocabulary with yours.

So, I smiled understandably and remained silent. understandably or understandingly? è Which one? They have different meanings, but both fit into the story just fine.

so I started shaking my head horizontally, horizontally? If it's vertically, it's nodding!

I knew I have stretched it a little bit too far. I knew I had è This is a good pick.

is this dentist’s office, I feel the punch line should be "Is this the dentist's office?" not 100% sure though.  è I know you are quite obsessed with “a”, “an”, “the”.  However they are totally dependent on a writer’s intention, not grammatically right or wrong principles as you may think.