It's well known (and documented) that PTFE fumes from cooking can be deadly to birds. I don't think "the most nontoxic" is anywhere near accurate, approximately or not.
Not that that same risk applies to dental floss (I don't think many people heat their dental floss to a few hundred degrees), but your statement was more general than that.
Pretty much anything produces toxic fumes if you get it hot enough. Air produces nitrogen dioxide, for example, water produces ozone, and table salt produces chlorine (and sodium vapor, of course, but that condenses before you have a chance to breathe it). Those fumes, which require temperatures far above cooking temperatures to form, aren't PTFE; they're a cocktail of nasty fluorocarbons which are bad for you too, just not immediately fatal the way they are for birds.
So "the most nontoxic" is pretty darn accurate. PTFE is substantially less toxic than air, water, table salt, cellulose, polypropylene, or pretty much anything else you're likely to put in your mouth.
You would have to heat the PTFE to almost glowing to make it emit fumes.
If you tried that with oil you would have an enormous cloud of smoke - and the smoke from the oil is MORE toxic than the smoke from the PTFE.
So yah, the most nontoxic is completely correct.
And BTW, it is far safer for your birds to use PTFE cookware vs oil because you would have to get the PTFE much hotter vs the oil for there to be any issue.
It's true that any foodsafe oil has a smokepoint lower than the temperature needed to degrade PTFE (https://en.wikipedia.org/wiki/Surface_chemistry_of_cooking#S... lists temperatures from 175 degrees for butter to 257 degrees for soybean oil), but in some cases only by a little bit.
I don't think it's necessarily true that cooking with PTFE is safer, even if the smoke is more toxic to birds, because the PTFE fumes are invisible, so you can kill your birds before you realize that there's a problem. It's not likely but it's possible.
I also don't think it's really true that you have to heat PTFE "to almost glowing". WP says PTFE starts to decompose around 350 degrees (science) and is already a health problem for birds above 250 degrees, killing parakeets at 280 degrees (after four hours of exposure, which was longer than it took burning butter fumes to kill the parakeets). See https://en.wikipedia.org/wiki/Polytetrafluoroethylene#Safety. Things don't start to glow until about 525 degrees, or a little hotter if they're very white.
The difference between 280 degrees and 525 degrees is even bigger than it sounds in terms of heat input. It's 145 degrees, yes, but at those temperatures radiation (in the infrared) is the dominant form of heat transfer, and radiation is proportional to the fourth power of temperature; at 280 degrees blackbody radiation is 5300 watts per square meter, while to get something up to 525 degrees you have to pump in 23000 watts per square meter, more than a factor of four.
The summary is that it takes four times as much heat per minute to make your teflon skillet glow as it takes to heat it up enough to kill your parakeet in four hours, which is about the same temperature that soybean oil starts smoking at, so if you have birds you might want to think about switching to cast iron, or at least always using abundant oil on your teflon so you're guaranteed to notice if you go outside the safe temperature region.
None of this is relevant to bike chain lube or dental floss.
I don't think the problem is only with smoke particles; I think gaseous fluorocarbons produced are sufficiently toxic to birds. (In humans they cause polymer fume fever, but the humans recover after a day or two.)
It's kinda funny to say this because one of the early problems with PTFE was the nerves in the hands of people handling PTFE-insulated aircraft wiring dying - due to residues from manufacturing in the PTFE. Sure, the polymer itself is non-toxic and non-reactive as can be. Everything that went into it is absolutely not. The way to minimize that is expensive process and quality control => don't use cheap polymers!
This was also the case with agent orange. Sloppy, rushed production led to it being absolutely full of unintentional contaminants from the manufacturing process.
