It is poo berries connected by fur, as others have said. Usually it will eventually stop, but it can cause fur impaction (wool block) which is often fatal. The digestive system gets blocked by all the fur, and they can't cough up hairballs like cats can. I lost a doe recently to fur impaction.
If you're just seeing a few of these, it should be okay. Definitely increase the amount of hay, and decrease the pellets. You can even stop the pellets for a few days. The hay really does keep things moving through the gut. It won't stop the dangling berries, because it is moving fur out of the gut... so it still ends up in the bunny berries. It will help keep the fur from collecting in the gut and causing impaction.
If you're seeing a lot of danglers, some say that feeding pineapple or pineapple juice can help break up or dissolve the fur. I would stop pellets altogether and free-feed hay, adding in some oatmeal (for added nutrition) after a few days if I was still seeing a lot of new danglers. I wouldn't add pellets again until the danglers were greatly reduced. If the rabbit stops eating, you'll probably lose it.
Sorry to come on a bit strong, just with losing Pearl so recently, I wanted you to know that while everything should be okay, you do need to keep watch on it. Clear the hanging berries daily so you can keep track.