Cesium is a highly reactive alkali metal. It’s high toxicity generally means its use is limited to atomic clocks and as a drilling lubricant (as a liquid alloy). It will react with water at even very low temperatures, which means care has to be taken in its use.
Brown Bears are large omnivorous mammals. They are capable of putting on a huge amount of weight to hibernate through winter months, eating almost anything. Encroachment of human habitation has led to more encounters with the creatures in the search of enough calories to last the winter. They can easily kill a man, if so inclined. Their hunger and danger makes them a good match for cesium.
Barium is a highly reactive element that is in general not found in nature. It’s mostly used for processing esters, x Ray contrast and making endothermic reactions. It’s actually often forms insoluble salts that don’t react with water, which makes pairing it with water creatures a little unusual. I couldn’t though go past the silly pun, so.
Barramundi also known as Asian sea bass and Australian sea bass. It’s a very highly sought after fish for fishing and as food. Though it is flakey and often has low flavor it’s often cooked with various flavors such as lime and garlic, and is a favorite fish for curry. It’s a undergoes sequential gender variation, changing gender often after one or two seasons as a adult male to adult female.