The technical details were 'over my head'. [=too complicated for me to understand]
She started to ask a question and then her voice 'tailed off'. [='trailed off']
His handwriting was so bad that we 'couldn't make heads or tails out of' it.
(..) . . -- I'd really love to stay, but-- Don't do that! That's my tail! That's my personal tail. You're gonna tear it off. I don't give permission-- What are you gonna do with that? . . (..)2001 Shrek