[jacquesm]

Look closely at the gear: the teeth are standing out on the side at right angles to the plane of rotation and are not protected by the geometry of the frame in any way.

That means that they will be very efficient at shredding flesh, far more so than a normal cassette which has the fastest rotating surface closest to the wheel.

Obviously you don't want to be in contact with either if you can avoid it.

As for the spokes: that's a problem that actually reduces above a certain speed because the spokes will start to act as a plane and throw you out before you can get anything properly wedged. At intermediary speeds they are really dangerous.

That's why it is important (especially for kids) to wear proper shoes on bikes and to put spoke guards on the rear wheel where feasible.

It doesn't take much to have serious injury of toes or heel, including damage to the Achilles tendon.