Ich habe einen kater is one way to say, auf Deutsch, that you have a hangover. This I learned from my hippie-ish German instructor, who was all purple flowing scarves and turquoise jewelry and looked to me a bit like an Austrian Alanis Morissette. This was on the day that the lesson focused on drinking, and (unsurprisingly?) I understood that lecture in its entirety. 

Luca, my German flatmate, injured his foot while running, and was asking me what a muscle strain is called in English. In German one says they have a muskelkater. 

I have not been able to ascertain what the Germans have against cats, or why they imagine cats are going around, sitting on various body parts, ailing them. 

This language lesson is really here for you to understand that this morning I woke up with a big old cat on my head.