Answer:
Carlson´s words show that he´s incapable of understanding George´s remorse over having just killed his best friend, Lennie. This is a reference to the title of the novel which was taken from Robert Burns' poem "To a Mouse".
Step-by-step explanation:
In the poem, Burns expresses his remorse over the accidental destruction of a mouse’s home while he was working in a field. A similar remorse George is feeling at the end of the novel.