When you have a girl on her back for anal intercourse, you pull out and rub your member on her belly button to make it brown then unload in her belly button. Hence the mud puddle.

A phrase to describe someone who is cognitively degenerating. Synonym of "going off the deep end". Can have varying degrees of severity.

Reference to the song "Hey You" by Pink Floyd. The line "and the worms ate into his brain" makes no sense in an otherwise linear and literal narration throughout the lyrics.