What Are the Strangest Features of Various Programming Languages?

Every programming language has its own unique quirks, such as weird syntax, unusual functionality or non-standard implementations -- things that can cause developers new to the language, or even seasoned pros, to scratch their heads in wonder (or throw their hands up in despair). Phil Johnson has rounded up some of the strangest — from the + operator in JavaScript to the trigraphs in C and C++ and indentation level in Python. What programming language oddities cause you the most grief?