Four, the perimeter of $\triangle A B C$ is $1992 \mathrm{~cm}$, a squirrel is located at point $P$ on side $A B$ (excluding points $A, B$). The squirrel first runs from point $P$ in a direction parallel to $B C$ to point $P_{1}$ on side $A C$, then immediately changes direction and runs in a direction parallel to $A B$. When it reaches point $P_{2}$ on side $B C$, it changes direction again and runs in a direction parallel to $C A$. When it reaches point $P_{3}$ on side $A B$, it changes direction again and runs in a direction parallel to $B C$, and so on. Can the squirrel return to point $P$? If it can return to point $P$, how much distance does it need to run at least?
(1) When point $P$ is the midpoint of $AB$, the little squirrel can return to point $P$ by running according to the requirements of the problem.

When it returns to point $P$ for the first time, the distance it has run is obviously the perimeter of the medial triangle of $\triangle ABC$, which is $\frac{1992}{2}=996(\mathrm{~cm})$.
(2) When point $P$ is not the midpoint of $AB$, the little squirrel can also return to point $P$ by running according to the requirements of the problem.

Because when the little squirrel runs to point $P_{5}$, it is easy to prove that $\triangle A P P_{1} \cong \triangle P_{1} P_{5} C$.
$\therefore \quad P P_{1}=P_{5} C$.
And $P P_{1} / / B C$,
$\therefore$ quadrilateral $P P_{1} C P_{5}$ is a parallelogram.
$\therefore \quad P_{5} P / / A C$.
This shows that when the little squirrel starts from point $P$, it can return to point $P$ for the first time after six turns.

At this time, the distance it has run is exactly the perimeter of $\triangle ABC$, which is $1992 \mathrm{~cm}$.

In summary, the little squirrel can return to the original starting point when it starts from point $P$ on the side $AB$ of $\triangle ABC$ (point $P$ is different from points $A$ and $B$) and runs according to the requirements of the problem. When $P$ is the midpoint of $AB$, the distance it runs to return to point $P$ for the first time is $996 \mathrm{~cm}$, and when $P$ is not the midpoint of $AB$, the distance it runs to return to point $P$ for the first time is $1992 \mathrm{~cm}$.