It's normal (= 普通, pronounced FUTSU) to boil one's younger brother in water from time to time.
|( が ) わ＊く||
to be boiling. Usually used with お湯, (hot water) as in, お湯が沸く ('The water's boiling!')
boil water ★★☆☆☆
literally, to boil some water. Figuratively; to seethe with anger or get too excited