Ear Worm: Quite a few to be found on their album. Try getting the whistled hook from "Pumped Up Kicks" out of your head upon hearing it… it's not easy.
Lampshaded in the "Call It What You Want" video; throughout it, Mark (Foster) is shown being stalked by a horde of rabid teenaged girls wearing shirts that spell out "Foster" collectively.
Nightmare Fuel: "Pumped-up Kicks," being known for its Lyrical Dissonance about gun violence, this troper was reminded of the Columbine High School Massacre, because many peoples' comments wondered if this is what the song's about (among other shooting attacks); due to this, I've done a lot more of research on the massacre... and now will never be able to listen to "Pumped-up Kicks" again without picturing Eric Harris' & Dylan Klebold's school shooting taking place.
Mark Foster was in high school when Columbine went down. This troper (one year older) can assure you: There's pretty much no way he wasn't thinking of it when he wrote the song.
There's an available instrumental version of the song. At minute 1:02, right before it gets to the chorus, you can hear a brief, distorted voice. It's hard to understand what it says. To me, it sort of sounds a bit like, "Leave here when you die." What's creepier is that I - nor even many of us - noticed this bit in the original!
Worse, it sounded like people were shouting during the chorus... turns out it was rhythmic clapping.