I'm a little ashamed to admit it, but:
Spoiler:
at first, I thought the gimmick was just that the person on the large poster was the person they were talking to in the street, and they didn't notice the fact.
Ha ha !! I laughed at them.
It took me a while to realise the person they were talking to was being swapped out.... (and I hadn't read the title at the top..)