Do the grouping $m^{3}-4m-m^{2}+4=\left(m^{3}-4m\right)+\left(-m^{2}+4\right)$, and factor out $m$ in the first and $-1$ in the second group.
$$m\left(m^{2}-4\right)-\left(m^{2}-4\right)$$
Factor out common term $m^{2}-4$ by using distributive property.
$$\left(m^{2}-4\right)\left(m-1\right)$$
Consider $m^{2}-4$. Rewrite $m^{2}-4$ as $m^{2}-2^{2}$. The difference of squares can be factored using the rule: $a^{2}-b^{2}=\left(a-b\right)\left(a+b\right)$.
