Through a laborious process of trial and error (I make the errors, Farkas undergoes the trials), I have discovered that Farkas puts up with my hitting him with swords, shooting him with arrows, and asking him to open doors that I know perfectly well are trapped with only mild complaints. However, the one time I accidentally set him on fire with one of J'zhargo's flame cloak scrolls, Farkas let me know in no uncertain terms that our friendship was over by killing me. So, there's an important boundary for you - don't set your friends on fire.
This can be really difficult when they keep insisting on getting between you and the bad guy.
It's Loredas night. You know what that means.
I let fly at a ghost with one hell of a sword blow. One of those ones where you really get your whole body into the swing, and you know your enemy is going down.
And then Farkas suddenly steps right into the path of my blade.
I've got enough time to curse, but not enough to pull the blow. It drops Farkas instantly. He doesn't even get out his usual, "Watch it, sister!" that's his typical response when I clip him with my blade or singe his hair with a misdirected Flame Shout. He just falls.
I glance down and see that he's on his knees and appears to be dry heaving. Good sign, I guess. Dead men don't vomit.
And that's the last thought I can spare for my shield-brother for a while, as the ghost comes at me. As insubstantial as it looks, the thing packs a punch, and what would have been a challenging fight with Farkas at my side turns into panicked flailing as I try to beat the thing back while pumping out healing spell after healing spell to deal with the hammering I'm taking from its axe.
"Only a fool would try to kill the dead!" it taunts me. I agree completely, but I don't remember it offering me the option of a cup of tea and a civilized chat.
At last, I kill the thing. And promptly trip over Farkas, who's still on the floor, and land face-down in the mixture of mud, blood, and ectoplasm covering the chamber floor. I spit and roll over to look at Farkas.
He looks like he's crawled halfway across the gateway to Sovngarde, and that the only reason he isn't all the way there yet is that my blow winded him so badly he doesn't even have the energy to die properly. I cast a healing spell on him, and we both climb unsteadily to our feet.
Farkas grins at me. "Wow, you hit hard."
"Farkas, do you remember that oath you swore when I joined the Companions?"
"I will stand at her back, that the world might never overtake us," Farkas recites.
It occurs to me that I've never told Farkas how much it meant to me that he would swear that, back in the days when most folk in Skyrim wouldn't have sworn to serve me a beer without spitting in it first. But now's not the time to go into that. "How about we try, 'I will stand at her back, so that I will keep out of the way of her sword arm'?"
"You've got it, shield-sister."