Just want to point out that being close to a source of radiation, and thus being radioactive, is not an evolution. It is just the condition of being irradiated. To produce radiation as a characteristic, it probably needs to break down molecules in such a way that leads to radioactive decay.

True. I get that. I read the OP in such a way that the mechanism is irrelevant, only the outcome. I'm not an evolutionary scientist by any means, but I can't see any reason why radiation would benefit the creature. Yes, radiation can kill or make something sick, but it's too slow. The creature already has a toxin for defense and Electrical shock for hunting. Why on earth would it have a much slower weapon in being radioactive?

I've heard rumors that I kind of doubt of fission-inducing bacteria.

I can't neccesarily see a reason why that would benefit the creature though.

If the frog had evolved in the radioactive environment (not unrealistic; there are plenty of species adapted to very specific environments) it may well have adaptations to cope with the radioactivity. Perhaps it stores up the radioactive material in its liver/kidneys/<some specialised organ>. This doesn't help it hunt or avoid being eaten, it's just a byproduct of a mechanism for surviving the radioactive environment. Of course it does then make the frog dangerously radioactive to everything else.

Please note that uranium, as found in natural deposits, is not radioactive in any significant way. It's so not radioactive that it can actually be used to shield against radiation, and it can do a batter job at it than lead, solely because it's denser. To make it radioactive to any noticeable degree, it has to undergo a very complicated and technologically advanced process.

@K.Morgan That's kind of what I was going for.

@vsz ...and even so, after being enriched, Uranium is still only radioactive enough to warrant a trefoil according to our radiation regulations, but nowhere near enough to actually irradiate anyone to any significant degree.

@vsz How about Radon or Radium, natural products of decay? I'm no expert on that sort of stuff, I was just thinking that all kinds of minerals get mixed up in rain runofff and such.

You could just make it need more potassium in its diet then a normal animal. That would give it a very slight radioactivity.

I think the radiation is just for cool factor. I can't see it being useful at all. What is the animal going to do? Defend itself by causing cancer in predators in 5-6 years? Yes very effective.

@TylerS.Loeper That's why I suggested it as an environmental factor, not as any sort of weapon. Though a frog that, when squished, yielded a 1 kiloton blast would be amusing as hell.

I'm not a nuclear physicist but it may be possible that the toad ingests enough fissile material to go critical becoming a bomb-pumped laser through a special organ/lens. This would require a rather large toad much larger than 780g and at the moment I can't imagine a biological structure to contain the fissile product for any amount of time. Critical mass value from: physics.stackexchange.com/questions/13325/…

@TylerS.Loeper Now that you mention it... can't radiation sterilize? Kill in 5-6 years is not very useful, but a bunch of frogs sterilizing other species over a few decades... I can see that being useful! Maybe they go near their gonads at night and if they wake up... well, that's what the "laser" is for. Stunning flash of bright light and run (hop) away!

@vsz there are entire areas of Australia that the native inhabitants referred to as the "sickness country" because of radiation poisoning from uranium deposits in the area. Small amounts unrefined may cause no issue, but when there's enough in an area it will have an impact.

Give it a double frog tongue. Tongues attack to prey and transmit electric charge like a tazer.

I can't see a double tongue working out (harder to aim), but a single tongue with a split end might be a better choice - as long as you place your zapper inside the tongue.

@RolandHeath An important difference between a deposit of uranium ore, and the uranium metal you can smelt out of it, is that the former will contain far more "daughter" elements produced by uranium decaying, many of which are much more radioactive than the uranium itself.

Gee I wonder what shape those colorful markings might take?

@DennisWilliamson a Green Deaths head, of course :)