Echidnas cool themselves off by blowing nasal mucus bubbles to keep their nose moist. When the bubble bursts, the moisture evaporates and cools the blood.

Echidnas' thermoregulatory system is quite primitive—they can't sweat, lick themselves, or pant with their tongues out like other mammals. So they had to invent it.
This also has a bonus function: keeping the nose moist allows for electroreception—echidnas find prey underground by detecting electrical impulses from the muscles of ants and termites. In other words, a wet nose is both an air conditioner and a hunting radar.