HNO = ENT

Don't worry. I'm not going to do algebra. "HNO" stands for "Hals-Nasen-Ohren-Arzt", which in English would be an "ENT" doctor or "ear-nose-throat" specialist.

What tickles me is that the order of the three parts of the body is the opposite way round in the two languages. Obviously, this is because they are listed in alphabetical order, but I still think it's funny that the lists are a "mirror image" of each other.