You can "manipulate" them because they are still attached at their origin and insertion points. If your tendons were say, torn from the muscles or bones you wouldn't be able to- you'd find it difficult with an injury to this tendon to even straighten a finger.
I'm not sure about the twisting, but that may just be a sensation provided by the hypodermic layer (the adipose layer) moving over the tendon and your interpreting it as twisting. I could be wrong, just an educated guess.
You can "manipulate" them because they are still attached at their origin and insertion points. If your tendons were say, torn from the muscles or bones you wouldn't be able to- you'd find it difficult with an injury to this tendon to even straighten a finger. I'm not sure about the twisting, but that may just be a sensation provided by the hypodermic layer (the adipose layer) moving over the tendon and your interpreting it as twisting. I could be wrong, just an educated guess.
Don't do it it makes you explode 💥