Ex12 2

$\def\abs#1{|#1|}\def\i{\mathbf {i}}\def\ket#1{|{#1}\rangle}\def\bra#1{\langle{#1}|}\def\braket#1#2{\langle{#1}|{#2}\rangle}\def\tr{\mathord{\mbox{tr}}}\mathbf{Exercise\ 12.2}$

Why do we consider the preparation of the cat state in Figure 12.6 to be fault-tolerant even though it includes two $C_{not}$ gates from the qubit on which the $Z$ measurement is made.