English idioms about brains

1. To have a screw loose

   Someone is a bit crazy, or is acting as if they've lost their mind.

   Elsewhere

   • FR Avoir une araignée au plafond
   • DE Nicht alle Tassen im Schrank haben
   • ES Faltarle un tornillo
   • IT Mancare qualche rotella
   • JA 頭のネジが外れている

2. It’s all Greek to me

   I can't understand any of it.

   Elsewhere

   • FR C’est du chinois
   • DE Ich verstehe nur Bahnhof
   • ES Me suena a chino
   • IT Per me è arabo
   • JA ちんぷんかんぷん

3. A fish out of water

   Someone who feels uncomfortable and out of place in unfamiliar surroundings.

   Elsewhere

   • FR Comme un poisson hors de l’eau
   • DE Wie ein Fisch auf dem Trockenen
   • ES Como pez fuera del agua
   • IT Come un pesce fuor d’acqua
   • JA 借りてきた猫

4. Have your head in the clouds

   To be lost in thought and not paying attention.

   Elsewhere

   • FR Être dans la lune
   • DE Mit den Gedanken woanders sein
   • ES Estar en las nubes
   • IT Avere la testa fra le nuvole
   • JA 上の空

5. Not have the foggiest

   To have no idea at all.

   Elsewhere

   • FR Donner sa langue au chat
   • DE Keinen blassen Schimmer haben
   • ES No saber ni papa
   • IT Non avere la più pallida idea
   • JA 見当もつかない

6. Compare apples and oranges

   To compare or mix up two things that don't belong together.

   Elsewhere

   • FR Mélanger les torchons et les serviettes
   • DE Äpfel mit Birnen vergleichen
   • ES Mezclar churras con merinas
   • IT Fare di tutta l’erba un fascio
   • JA 月とすっぽん

Phrases in bold with a red marker are written up. The rest are waiting for their own page and a check by a native speaker.