I have a very simple obj file:

```
v -2.22045e-16 -0.291306 -2.22045e-16
v -0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 -2.22045e-16 -0.24339
v -2.22045e-16 -2.22045e-16 -0.24339
v 0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 -0.291306 -2.22045e-16
v -2.22045e-16 -2.22045e-16 -0.24339
v -0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 0.291306 -2.22045e-16
v -2.22045e-16 -2.22045e-16 -0.24339
v -2.22045e-16 0.291306 -2.22045e-16
v 0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 -0.291306 -2.22045e-16
v -2.22045e-16 -2.22045e-16 0.24339
v -0.24339 -2.22045e-16 -2.22045e-16
v 0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 -2.22045e-16 0.24339
v -2.22045e-16 -0.291306 -2.22045e-16
v -0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 -2.22045e-16 0.24339
v -2.22045e-16 0.291306 -2.22045e-16
v 0.24339 -2.22045e-16 -2.22045e-16
v -2.22045e-16 0.291306 -2.22045e-16
v -2.22045e-16 -2.22045e-16 0.24339
f 3 2 1
f 6 5 4
f 9 8 7
f 12 11 10
f 15 14 13
f 18 17 16
f 21 20 19
f 24 23 22

```

As you can see, there is no `vn` command. However, if I open it in meshlab and turn on the vertex normal rendering, it shows vertex normals (and some normals not attached to vertices).

Why does this happen?