There are times when people just don't feel like doing anything. They rather sit quietly by themselves and do nothing. Staring into space, contemplating their circumstances, calculating their actions... Or whatever that was passing by before them or popping up in their mind. I think it's possible that nothing could get a reaction from those who choose to ignore their surrounding.
Except, maybe for food.
Yes, you might disagree but it is a wonder what food could do to your senses.