Worm gearbox question (video included)

[Alice24]

https://youtu.be/b4b-hqcVUYE

As you can see from the vid above, if I hold the output shaft strong enough, it doesn't rotate, but I still hear regular output noise from the stepper motor, so it seems that the gears are spinning normally. What is in fact happening? Does the internal cylinder have a disengagement mechanism from the worm's wheel?

 

[3DDave]

The stepper motor is skipping steps because the motor is stalled out. In most motors this causes overheating, but in stepper motors, they just make a growling sound that will depend on the inputs from the stepper driver.

 

[Alice24]

Weird, really? I think I'm hearing the sound of the worm gears still spinning, or is it the sound of them "struggling" to spin which sounds almost the same as them spinning? Because the motor stalling sound is different IIRC

EDIT: Nevermind, just checked the sound of it stalling without the worm gear. Yep, you're right, that's the stall sound alright