Translation sphere

Translation Spheres are special translation devices carried by Ood that have been enslaved by humanity. In order to use it, an Ood presses a button on the sphere, and speaks into the tube, which must be in their mouths for the sphere to work. A sphere remains permanently fixed in the mouth of its owner via this tube. The tube is linked to its owners body in the same way as their smaller brain once was since only enslaved Ood have translation spheres. (DW: Planet of the Ood)

These translation spheres can be clipped on the Ood's shirt when they are not holding them. (DW: The Impossible Planet / The Satan Pit)

As a weapon
Rebellious Ood somehow managed to turn the spheres into deadly weapons. Ood Operations had no idea how this was done, and indeed did not initially notice it, atributing deaths to heart attacks and industrial accidents.

There are two ways the Ood were seen using the sphere as a weapon. Either they threw it at victim, let it spring back, and caught it, or they could simply place it on someone's forehead. The effect would be the touched area lighting up and crackling with electricity, and the human would drop to the floor, dead. (DW: The Impossible Planet / The Satan Pit, Planet of the Ood)

Whether this is a normal feature or a trait given to the Ood by the Beast is unknown but since the spheres are used as weapons by the Ood on the Ood-Sphere in 4126, as well as the fact that the spheres are connected to the Ood where they once had a smaller brain, it is likely that the Ood always had the ability to use spheres as weapons, possibly using their telepathic powers to damage a victims brain via a sphere. (DW: Planet of the Ood)