Okay... do you know what can happen if you short-circuit a pencil battery while holding it in your mouth?
A 10-year-old boy from India found this out the hard way, as described in an article by Kumar et al. (2013)... The battery can EXPLODE and pretty much destroy your mouth and face.
This unfortunate kid tried to short-circuit three low-voltage batteries with a wire while holding them in his mouth. He was twisting the wire with his teeth when one of the batteries exploded. The gory result can be seen below. Yes, I know this is a drastic photo. Pretty much the entire lower half of the face is gone, leaving a gaping bloody ruin.
The explanation for this accident is that low-voltage batteries contain a high amount of energy. The low internal resistance of such a battery, when short-circuited, permits a heavy flow of current. The short circuit instantaneously vaporizes a miniscule portion of the wire at approximately 2000 K, resulting in a blast in a closed cavity causing sudden rise of intraoral pressure which can lead to extensive tissue damage in and around the mouth.
Even drastic facial injuries are frequently not life-threatening unless associated with other injuries of the skull and/or airway, causing brain damage or breathing trouble. This particular patient was immediately rushed to the hospital, suffering from shock, severe bleeding and breathlessness. At assessment, he had a pulse of 120/min, respiratory rate of 36/min, and blood pressure of 86/60 mm Hg. Because lack of support to the tongue was causing respiratory distress, an emergency tracheostomy was done under local anesthesia, after which the wounds were cleaned thoroughly and dressed. A feeding tube was also inserted. After stabilization and all routine blood investigations, a 3D CT scan of the head was performed, showing the full extent of the damage:
The patient had lost the arch of the upper jaw along with all the upper teeth. His lower jaw was fractured and the lower segment, carrying all incisors and canines, was also lost. Soft tissue injuries included loss of the upper and lower lips, skin of the chin region, partial loss of both alae of the nose, lacerations all around the mouth and abrasions on the chest and right arm and forearm. Debridement of nonviable tissues and daily dressing was done for a week, during which the boy was given three blood transfusions.
After stabilization, the patient was taken up for surgery under general anesthesia. A cap splint with zygomatic suspension was done for the upper jaw, the residual mandibular segments were wired together and covered with a right-sided deltopectoral flap. A split skin graft was used to cover the donor site. Here is an early postoperative photo:
While the flap coverage was successful, more surgeries will be needed to debulk the flap, reconstruct the upper lip and enable the patient to eat normally instead of being fed through a tube. In the following postoperative picture, the flap has been detached but the tracheostomy is still there. Obviously, the child has been disfigured for life.
All images from: Kumar et al. (2013)
So... please, folks, don't fool around with batteries, recharge them, toss them in a fire or let your kids play with them. The familiar warning that an improperly handled battery "may explode or leak" is not to be taken lightly!
Kumar V, Singh AK, Kumar P, Shenoy YR, Verma AK, Borole AJ, Prasad V. (2013) Blast injury face: An exemplified review of management. Natl J Maxillofac Surg. 4(1): 33–39.