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.
(..) -What have we done? -Great! Now I have guilt. We're almost there! Rocky, the ramp! Look out! Quick! Hold onto my tail! -Attaboy, Slink! -Oh! Woody! Woody! Speed up! -Speed up! -The batteries! (..)1995 Toy Story