I heard an interview with Max Brooks where he talks about survival in a zombie apocalypse and he mentions expending energy. I couldn't tell what their plan was, but Carol was up for most of the night with Judith/keeping watch before we saw the house and we know Tyrese wasn't sleeping well. I'm not sure if Tyrese ever took over Judith/watch duty. Tyrese continued to have trouble sleeping. Then there is the emotional toll of the day, finding Mika dead, having to take care of Lizzie. Killing the rail walker might have been a bit too much. They have to be exhausted. They never did kill the deer, so they only had pecans/pecan cookies to eat. Not what I would consider a balanced diet. And that's not taking into account what they had to eat and drink before the house. As Rick said in the comics, they are the walking dead, they just don't know it yet.