Bobblehead Ch 4 p99: Alien doesn't get pushed around by the bullets

I am hoping someone can help me. All has worked thus far (starting Chapter 5 next) except I noticed on page 99 (in the physical copy of the book) that the bullets are supposed to push the alien around. They don’t go through him, but they don’t make him move at all. Can anyone help me fix this? I don’t want to go too much farther in case this will turn into a huge problem later.

@vegetarianzombie Do you have any feedback regarding this? Thank you - much appreciated! :]

Problem solved. I missed the instructions at the bottom of page 90 about adding a rigidbody to the Alien.