Funhouse

 is a song from the Season 3 episode "Misperceived Monotreme". It was played as Candace, Jeremy, Phineas, Ferb, Isabella, Baljeet, and Buford explored the fun house the kids' built.

Lyrics
Well you think it's a chair

But it's growin' curly hair

And your sister's unaware

That she's floating in the air

You're livin' in a funhouse, baby

You're livin' in a funhouse, don't mean maybe

A million doors in the hall

And the table's on the wall

And the bathtub is your bed

And a floating baby head

You're livin' in a funhouse, Lawrence

So you'd better get some optical illusion insurance

The floors are steep, you'll never sleep

Your mother calls through the rubber walls

Liftin' up a feather that weighed a ton

Don't need to rent a funhouse, make your own house fun! (Your own house fun!)

You're livin' in a funhouse, baby

You're livin' in a funhouse, pass the gravy

And while we're on the subject, meet my friend Davy

He was in the navy and his hair is wavy

We're livin' in a funhouse, mama

We're livin' in a funhouse, quite the drama

And while we're on the subject, that Peruvian llama's

Wearing my pajamas and I know that I'm-a

Just livin' in a funhouse, baby!

Background Information

 * During the line "Lifting up a feather that weighs a ton", Phineas and Ferb are lifting weights marked 1,000 pounds. One ton is 2,000 pounds, so combined, they are indeed lifting a ton (or its featherweight equivalent). However, the feather weighing a ton may just be a figure of speech, not actually weighing exactly 2,000 lbs.
 * The Giant floating baby head is mentioned in this song.

Allusions

 * The lyrics 'baby' and 'don't mean maybe' seem to allude to the classic 1925 song Yes Sir, That's My Baby.
 * Davy in the navy could allude to the Billy Joel's song Piano Man.
 * The Peruvian llama wearing pajamas could allude to the comic book superhero Pajama Llama from the Disney Channel series The Emperor's New School, which alludes to the "llama in pajamas" from Down By the Bay.