I had a decapitated head and used a wooden spike to spike it into the ground as follows:

Behead, campfire to shrink head, plant spike, spike head

My guess is that this is communes only, being that now I can only make "trophies"

Argh, why can't we do both?

Bleh, yeah, I really wanted to be able to shrink heads, too. I much prefer shrinking+spiking to just being able to make trophies.