put your finger on
US /pʊt jʊər ˈfɪŋ.ɡər ɑːn/
UK /pʊt jʊər ˈfɪŋ.ɡər ɑːn/

1.
mettre le doigt sur, identifier précisément
to identify exactly what is wrong or what has caused a problem
:
•
I know something is wrong, but I can't quite put my finger on it.
Je sais que quelque chose ne va pas, mais je ne peux pas vraiment mettre le doigt dessus.
•
The manager couldn't put his finger on why sales were declining.
Le gérant ne pouvait pas mettre le doigt sur la raison de la baisse des ventes.