Helium: It is an inert gas that is lighter than air. It is non-flammable.

A pacemaker is a medical device used to regulate the heartbeat in individuals with abnormal heart rhythms (arrhythmias). It is often implanted in the chest to help control the heart's rhythm and treat conditions like bradycardia (slow heart rate) or other rhythm disorders. Pacemakers are typically prescribed by cardiologists, specialized doctors who diagnose and treat heart-related conditions. The decision to implant a pacemaker is made by a healthcare provider based on the patient's specific medical condition and needs.

Actually, the locomotor part of a hydra is not its tentacles. Hydras move by a remarkable way called "looping." They attach one end of their body to a surface and then release the other end, allowing it to move and attach again. This looping movement is facilitated by the contraction and expansion of the body, rather than the use of tentacles. Tentacles are specialized structures primarily used for feeding and defense in hydras.