You can use parenthesis around any expression, as in most languages. eg something like:

    bank balanceOf: (bank findAccount: #savings)

However, parens aren't necessary when a nested message takes no arguments, or uses a binary selector. eg:

    bank withdraw: 3 + 4 from: user checkingAccount

There are 3 messages here.

    1. 3 + 4 (execute method + with argument 4)
    2. user checkingAccount (getter with no arguments)
    3. bank withdraw: <result of #1> from: <result of #2>

Think like arithmetic. 2 times: (3 plus: 4).