While I was messing around with the dipping poison enchantment, I accidently hit the pole that a geomancer summoned. You would probably expect it to just hit the pole, and disappear, right?  But no, it gives the pole the effect when it hits a mob. it turns green and starts to "take damage" it does the damage  effect, but doesn't show the damage. My guess is that the pole is an entity, like the mobs in game. this makes it take poison "damage", probably take fire "damage" and also the player can shoot a corrupted beacon beam through it.  to reproduce, make a geomancer summon a pole, and shoot a poison arrow at the pole. 

sadly, I am not a computer expert(Not at all, I'm only ten) so I can't take a screenshot