Bamboo, root, or culm thats gone back under?

[cordyman]

Never seen this before, its on my Robusta Campbell, is it just a large root, or is it a culm that was surfacing hit another culm perhaps then went under again to resurface elsewhere

[Adam D]

It's quite normal mate.

They call them "dolphin" culms.

I guess it is a sign that they are quite happy