Object3D.lookAt() in instanced meshes not as expected? - three.js

Question

I'm building a particle system in which particles have directions they are pointing at and I want to reflect that in an instance mesh I use to present them, but something is not quite working... It seems that the center of rotation and/or the up axis are not quite right, and despite me console logging stuff I could not find the problem. Here's the code:
const Particles = (particleSystem: TparticleSystem) => {
const mesh = useRef<THREE.InstancedMesh>(null);
const light = useRef<THREE.PointLight>(null);
const dummy = useMemo(() => new THREE.Object3D(), []);
const pyramid = useMemo(() => {
return {
vertices: [1, 0, 0, 0, 0, 1, -1, 0, 0, 0, 0, -1, 0, 2, 0],
indices: [0, 1, 2, 2, 3, 0, 0, 4, 1, 1, 4, 2, 2, 4, 3, 3, 4, 0],
};
}, []);
useFrame(() => {
if (particleSystem !== undefined) {
particleSystem.update();
particleSystem.move();
particleSystem.particles.forEach((particle: Tparticle, index: number) => {
dummy.position.set(particle.pos.x, particle.pos.y, particle.pos.z);
dummy.lookAt(vec().copy(particle.pos).add(particle.dir)); // rotating weird
dummy.scale.set(1, 2, 1);
dummy.updateMatrix();
// And apply the matrix to the instanced item
if (mesh.current) mesh.current.setMatrixAt(index, dummy.matrix);
});
if (mesh.current) mesh.current.instanceMatrix.needsUpdate = true;
}
});
return (
<>
<pointLight ref={light} distance={40} intensity={3} color="lightblue" />
{particleSystem !== undefined && (
<instancedMesh ref={mesh} args={[, , particleSystem.num]}>
<polyhedronBufferGeometry
args={[pyramid.vertices, pyramid.indices, 1, 0]}
/>
<meshBasicMaterial
color="#2596be"
wireframe={Math.random() > 0.5 ? true : false}
/>
</instancedMesh>
)}
</>
);
};
I feel like maybe this is something to do with local and world coordinates, but I don't quite understand it.
Oh! and this vec stuff is just
const vec = function (x = 0, y = 0, z = 0) {
return new THREE.Vector3(x, y, z);
};