I would think it is a worm of some kind. If you cut it open and find a worm, a picture might help determine which kind of worm it is, then someone could tell you what to do to prevent them.
Invasive plants are Earth's way of insisting we notice her medicines. Stephen Herrod Buhner
Everyone learns what works by learning what doesn't work. Stephen Herrod Buhner
My first bit of advice is that if you are going to be a mime, you shouldn't talk. Even the tiny ad is nodding: