A $1 \mathrm{GeV}$ muon neutrino is fired at a $1 \mathrm{~m}$ thick block of iron $\left({ }_{26}^{56} \mathrm{Fe}\right)$ with density $\rho=7.874 \times 10^{3} \mathrm{~kg} \mathrm{~m}^{-3}$. If the average neutrino-nucleon interaction cross section is $\sigma=8 \times 10^{-39} \mathrm{~cm}^{2}$, calculate the (small) probability that the neutrino interacts in the block.