Identify the error in this 3D plot code snippet:

Identify the error in this 3D plot code snippet:

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)
x = [1, 2, 3]
y = [4, 5, 6]
z = [7, 8, 9]
ax.scatter(x, y, z)
plt.show()