What would happen to animal cells if they had cell walls like plant cells?

If an animal's body were made of plant cells, the animal would be very stiff and unable to move easily.

Well if you mean animal cells having a rigid cell wall like that of plant cells a few things would happen: ... Cells would not be able to transport material in and out of the cell as easily with a cell wall (endocytosis and exocytosis especially would be hampered).