Not all non-Newtonian fluid is toxic. A good example of this would be the synovial joints such as your knee making use of a non-Newtonian fluid (synovial fluid) There are a few that would be...
Toxic markers are like poison, once they are on you're skin you're blood wil turn purple and you might risk dieing or injury, but non toxic markers are such as from crayola or washable expo markers...
Yes and no. Carbon dioxide is a waste product formed from respiration. It is the build up of this that makes you want to take a breath when you are holding your breath, not the lack of oxygen....