Something weird's going on 'round here,
Gotta get me some еvidence!
Some strange goings-on happenin' on the back lawn
And it's gettin' too intense.

'Cause you're not Ferb! No!
And I'm disturbed!
'Cause you're not Ferb!

You've got the same colored hair and his savoir-faire
And his zany serenity!
Though it's not conclusive something elusive
Says you stole his identity!

Cause you're not Ferb! No!
You're not Ferb! No!
You're not Ferb!
You're not Ferb!
You're not Ferb!
You're not Ferb!
You're not Ferb!
You're not Ferb!
You're not Ferb!

http://phineasandferb.wikia.com/wiki/You're_Not_Ferb