using dashes
There was a loud boom--what a fright--from the back of the theater.
We all turned around--I even jumped up--to see what it was.
It was part of the play--imagine--that meant to add suspense.
The first two are fine. The third one reads funny; I think the second dash needs to be moved. Do you see where? Read the sentence out loud.
I don't know if your text addresses this, but I'd also add an exclamation point in each one. Here's how:
There was a loud boom -- what a fright! -- from the back of the theater.