is there a way to use multiple penetrating tentacles? When you try to insert another you end up letting go of the current one
When you move it in and out a bit in a steady rhythm, then the game will recognize the pattern, which is indicated by both arrows turning bright. When you then release, then the tentacle will stay in and continue the motion with the same speed and depth.
I wonder if others also have trouble figuring that out. If so, I might have to tutorialize that somehow.