Nouns ending in -elle are usually feminine.
The suffix often forms a diminutive feminine.
Is cervelle masculine or feminine?
lacervelle
The rule behind it
95.1% of -elle nouns are feminine
In context
Elle fournit la cervelle et lui les muscles.
She provides the brains and he provides the brawn.
Tom s'est fait sauter la cervelle.
Tom blew his brains out.
Je veux me faire sauter la cervelle.
I want to blow my brains out.