Matplotlib: Animate multiple scatter plots

I'm trying to create an animation which shows multiple particles moving around.

If I have one particle with one array giving the positions of that particle in each step of the animation, I get it to work (mostly thanks to extensive help from other answers I found here on stackoverflow).

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation


positions = np.array([[2,2],[3,3],[4,4]])


def init():
    scatterplot.set_offsets([[], []])
    return [scatterplot]

def update(i, scatterplot, positions):
    scatterplot.set_offsets(positions[i])
    return [scatterplot]

fig = plt.figure()

scatterplot = plt.scatter([], [], s=100)
plt.xlim(0,5)
plt.ylim(0,5)
anim = animation.FuncAnimation(
fig, update, init_func=init, fargs=(scatterplot, positions), interval=1000, frames=3,
blit=True, repeat=True)
plt.show()

But I cannot figure out how to add more particles to the same animation. Let's say I want to add a second particle with positions

positions2 = np.array([[2,1][3,2][4,3]])

and have it move around in the same scatter plot, how do I manage that?

I'm a matplotlib newbie, and have been googling furiously to no avail, will be very grateful for any help :)

EDIT: I figured it out eventually, just a matter of formatting the data correctly.

positions = np.array([[[2,2],[2,1]],[[3,3],[3,2]],[[4,4],[4,3]]])

Where the array contains all the positions in step one, then all the positions in step two etc. works. I'd prefer to get one color pr moving point, to keep track of them, but at least it works now.