Horses will die if they mouth breathe at speed because it disrupts efficient oxygen intake.

“a horse will die at speed if you mouth breeze i've looked into the physiology and everything on that they they their their nose is designed so that as they're running because their diaphragm actually works it's like this you know works as a major piston so when they land it drives the air out and when they gallop it drives the air in and it's a perfect shot from the nose to the base of the lungs they open that mouth and it ruins that and then they can actually they'll hyperventilate so quick that it's it's like it's a death sentence it's fascinating”