The expression \( x^4 - 4x^2 \) can be factored to make it simpler. Here's the step-by-step process:

1. **Identify a common factor**: Notice that both terms have a common factor of \( x^2 \).
\[
x^4 - 4x^2 = x^2(x^2 - 4)
\]

2. **Factor the quadratic expression**: The expression inside the parentheses, \( x^2 - 4 \), is a difference of squares. The difference of squares can be factored using the formula \( a^2 - b^2 = (a - b)(a + b) \). Here, \( a = x \) and \( b = 2 \).
\[
x^2 - 4 = (x - 2)(x + 2)
\]

3. **Combine the factors**: Substitute back into the original factorization.
\[
x^2(x^2 - 4) = x^2(x - 2)(x + 2)
\]

So, the factored form of \( x^4 - 4x^2 \) is:
\[
x^2(x - 2)(x + 2)
\]

This is the fully factored form of the given polynomial.