Is that they say his and byes at such regularity that it has become a switch in their brain nerves and muscles to put up a hand or raise an eyebrow automatically when they see one. It's almost robotic. All these happen so fast that before you can think of what else to say, both of you have walked past each other. And in the circumstances where you've got to say something, partly because the situation calls for it but largely because both of you happen to be stationary, you say strange and silly things.

(Prata shop. 3am)

He - (waving at me) Me - (raise eyebrow to acknowledge, continue eating prata) He - 一个人读书啊? Me - 没有, 在吃 supper. 要回了. He - OH. 你住 hougang hor? Me - 没有, 我住 Hall 5. He - Orh.