Walking Dead Season 2

[Blak Smyth]

My wife asked me a question and I didn't know the answer:

"Do you think Shane left Otis for dead to give him more time to escape?"

or

"Did Shane leave Otis as revenge for shooting Carl?"

I think if he had left him to escape he would have shot him once and been gone. Because he began to beat Otis I believe it was meant to be revenge.
What do you guys think???