10 Small Details You Only Notice Rewatching How I Met Your Mother
1. The Background Couple
In Season 9's The Rehearsal Dinner, Robin suggests getting married in Canada. Just as they do every time she mentions her home and native land, her friends spend an absurdly long time making fun of the Great White North, often involving mittens, Tim Hortons, and repeating things in French.
One hard to notice background gag shows just how long a time the gag spend making Canada jokes. If you look closely, you can see that, throughout their jokes, a man and woman meet, start dating, propose marriage, celebrate their pregnancy, have a drink with the fully grown graduate son, and mourn that son in their old age. The creators draw no attention to it, but watching the progression of this couple's life is funnier than any of the gang's Canada jokes, which is exactly the point.
How I Met Your Mother is a strange show, since it takes nine seasons for one couple to meet, but another couple's entire life flies by in less than a minute.