The hydra towers are shooting its poison at my own waves. I don’t think it’s doing damage, but I can clearly see the animation and splash damage left on the ground in the other direction.
The Hydra Tower should shoot its first poison lane in the direction of the enemies. While there is already poison on the ground where the enemies are, it will start shooting into random directions. The defending units do not take any damage from it. It even protects them in a way because it damages enemy units (and the Hero) who come close to attack them.