Abstract: A hand held device for injecting a fluid (such as a vaccine) or an object (such as a transponder) beneath the skin of an animal, the device comprising a mounting (2) for receiving a conventional hypodermic syringe (5,6,7), a weight (7) (which may be part of the plunger fitted within the syringe) for acting on the plunger (7) of the syringe and a slapping plate (3), being arranged so that when the device is swung into contact with an animal so the needle (6) of the hypodermic syringe pierces the animal's skin and the device is brought to a sudden halt as the plate (3) slaps against the animal, the momentum of the weight (7) acts to push the plunger (7) into the syringe and so propels the fluid or object held therein into the animal.