From Joshua Greene's Homepage:
"A runaway trolley is hurtling down the tracks toward five people who will be killed if it proceeds on its present course. You can save these five people by diverting the trolley onto a different set of tracks, one that has only one person on it, but if you do this that person will be killed. Is it morally permissible to turn the trolley and thus prevent five deaths at the cost of one? Most people say yes. 
Now consider a slightly different dilemma. Once again, the trolley is headed for five people. You are on a footbridge over the tracks next to a large man. The only way to save the five people is to push this man off the bridge and into the path of the trolley. Is that morally permissible? Most people say no.These two cases create a puzzle for moral philosophers: What makes it okay to sacrifice one person for the sake of five others in the first case but not in the second case? But there is also a psychological puzzle here: How does everyone know (or 'know') that it's okay to turn the trolley but not okay to push the man off the bridge? My collaborators and I have collected brain imaging data suggesting that emotional responses are an important part of the answer."
I haven't read the full versions of the papers yet but I'm surprised that apparently the first choice is considered to be a cognitively easy one whereas the second one isn't. Where are these people coming from? The CTU training institute that spawned Jack and his ilk?
Anyhow, something to think about.
