Treatment in Essen

Listen up, dummy. 'Essen' is the German word for 'to eat' or 'food'. The joke plays on 'treatment' as in getting a 'treat' (food). Instead of going to America for a 'treat-ment', they stayed in 'Essen' (eating) and then 'left' (like leftovers). It's a bilingual pun, which is why your single brain cell couldn't process it.