I mean that not all living organisms have to be composed of the same materials as we are. Since arsenic is toxic to us, maybe other elements can be composed into a living organism, right? Maybe some organism use other unusual elements? Other organisms could form from toxic elements if this one can use arsenic. The universe is a big space. Something or someone else could be wondering the same thing. They may think "Were made of helium, aluminum, krypton, einsteinium, and californium. Oxygen may be toxic to everything on our planet, but maybe some other organism needs it to survive." I know I might sound very crazy, but its the truth. It could very well be possible.