In one hand he held a bottle of liniment and with the other he rubbed his spine.
Noiselessly Lennie appeared in the open doorway. Crooks stiffened and a scowl came on his face."You got no right to come in my room. This here's my room. Nobody got any right in here but me."
"Come on in and set a while," Crooks said. "'Long as you won't get out and leave me alone, you might as well set down." His tone was a little more friendly.
His back pain signifies the pain that black people felt from slavery, the liniment being something that soothes the pain a little bit, but can't cure his pain (slavery becoming illegal in 1787, but not fully until 1808.)
"This is just a nigger talkin', an' a busted-back nigger. So it don't mean nothing, see?
Crook's room is the only place that he is really allowed to be in when he isn't working. It therefore feels like an invasion of space, if someone enters without asking, especially if that person is white, because they have their own place to stay, where he is not allowed to go, since he was segregated as a result of his skin colour.
"I seen it over an' over- a guy talkin' to another guy and it don't make no difference if he don't hear or understand. The thing is, they're talkin', or they're settin' still not talkin'. It don't make no difference, no difference."
Upon learning that Lennie isn't trying to invade his space, and just wants to talk to him, (since he doesn't care if Crooks is black) Crooks relaxes a bit and allows him to come in. This is similar to when black people were hopeful things were going to get better within their lives after the 14th amendment came about.
Crooks sat on his back and looked at the door for a moment, and then he reached for the liniment bottle.
Crooks feels as if his opinion doesn't matter in any way since he is black, as that is the way his race are treated, mainly referring to Louisiana banning most black people from having the right to vote (1898)
This is Crooks explaining that company is company, it doesn't matter who it is. It shows his desperation for company, since he has been so lonely for so long as he is segregated for the colour of his skin, much like when black people were segregated in streetcars (1902)
Crooks ends up in exactly the same place here, as he started the chapter in, which represents the whole black community in going forward, but always having some ort of step back, which causes them to end back where they started, during that time.