know (one's) beans

To be knowledgable about and/or very familiar with something. I had no idea you were such a good piano player—you really know your beans!

Name	Pronounced	Usage
Moshe	-	Hebrew, Biblical Hebrew
AmÉ	-	Medieval French
Theophilos	-	Ancient Greek
Katrijn	kaht-RIEN	Dutch
Culhwch	KEEL-hookh (Welsh)	Welsh, Welsh Mythology
Emelina	-	Spanish