I am attempting to study an armature to understand how it was rigged, and I'm having trouble understanding why the bones move like they have IK when there are no constraints on the bones.
There is a shoulder bone, an upper arm bone, a lower arm bone, and a hand bone. When I move any of these bones, all of them move like they have IK on them, but there are no bone constraints. A dotted yellow/orange line appears and connects from the bone I am actively moving to the shoulder bone, which I know has something to do with it, but I have been googling what that is to very little success.
Here are the bones at rest position:
Here are the bones when I move the upper arm bone, keep in mind I can move any of the four bones and get the same bendy arm result.
None of these bones have constraints.
What is causing the bones to move like this? Is there a setting somewhere that I'm missing?
EDIT: I added the blend file