People used to approach me in the street with a loud greeting and a smile and I would open my mouth to answer them, and then they would walk straight past me and I would realise they were talking on phones connected by wires to their ears.
Then I would shut my mouth and determine not to be fooled again by such an obvious if unintended trick. But I always was.
Now it's different. No-one looks at you any more because they're walking down the street with their heads down, gazing into 'apps', a word I don't like.