Know something backwards and forwards

Know something like a book / Know something like the back of one's hand


Conoscere qualcosa a menadito

Sapere qualcosa come l'Ave Maria


Meanings
To know something extremely well

Examples
The leading actor of the school play is down with the flu. Luckily George knows the part backwards and forwards and can replace him in no time
Il protagonista della recita scolastica ha l'influenza. Fortunatamente Giorgio conosce la parte a menadito e lo può sostituire all'istante

The student read and repeated the poem over and over until he memorized it to perfection. Now he really knows it backwards and forwards
Lo studente ha letto, riletto e ripetuto la poesia fino a memorizzarla alla perfezione. Adesso la sa come l'Ave Maria