A forest where 1 in every 100 tress is a Flesh eating tree hat is indistinguishable from regular trees, until it attacks one of your colonists that is. After that, you'd better remember which it was because nothing outwardly obvious would distinguish it.
That would make the choice of going far into the forest scary and thus interesting.
Similarly: quicksand.
That would make the choice of going far into the forest scary and thus interesting.
Similarly: quicksand.