They are all over the garden.

What are they?

The seed from European Beech(Fagus sylvatica)

These fuckers used to be all over my yard until I convinced the city into removing the tree. They leave little dents and holes everywhere after they break down.

Edit: Sugar Gum pod

That looks linke something H.R Giger could have come up with.

You're right, they also make a satisfying crunch when you step on them on the sidewalk

These motherfuckers will go straight through the sole of your shoe, or puncture your bike tire. The most hateful plant I've ever known

Biblical accurate sea urchin.

Yeah those seem worse!

Walking in my yard for more than 30 seconds has my shoe soles crunching with these fuckers when I come inside. Get to spend the next few minutes picking them out. And no matter how thorough you are, chances of these being on an indoor floor are never zero. Hard to get rid of and just all-around nasty, agreed.