A Pea in a Boxcar

I was thinking about writing some responses to questions about writing.  I was thinking these thoughts in the middle of the night when one would  be  better served by sleeping.  At any rate, the expression "If you had a brain, it would rattle around like a pea in a boxcar" popped into my -pea- brain.

When we kids would make this remark to one another it was well-understood that the comparison was one of volume, i.e., relatively speaking, a brain in your cranium would be microscopic in size.

Then, remember this is in the middle of the night, my pea started processing the physics of a literal pea on the floor of a literal boxcar.  I finally dozed off when I realized that for some of us the car has been on a siding so long and the pea is so desiccated and sere that no amount of jostling, jolting, or starting and stopping the car would any longer elicit any kind of response from the pea.