@Background Pony #EE41
I think what he means is that the heat radiation (infrared) can travel undisturbed because of less denser air and would easier cause burnings.
@Commander117
You are talking about beings that can break the barrier of sound without desintegrating themselves, or even noticing. How much heat you think it generates flying at such speeds?
Naturally, Derpy is unfazed, when in reality being that close to flames of that size that high up in the atmosphere, (it’s easier to burn because the air is clearer, i.e. less particulates in the way of heat) you would likely get some severe 2nd-degree burns at the very least.
The marshmallow is funny though, and I don’t mean Rarity.