Why are some traps visible and some invisible?

I don't have any specific champion in mind when I'm asking this, but I just got curious, why are some traps visible and others invisible? Visible traps: {{champion:51}} {{champion:57}} {{champion:76}} Invisible traps: {{champion:35}} {{champion:17}}

We're testing a new feature that gives the option to view discussion comments in chronological order. Some testers have pointed out situations in which they feel a linear view could be helpful, so we'd like see how you guys make use of it.

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