So, I have a couple of those betta logs from Petsmart. Buddy has had one in his tank for some time now, and I never noticed any issues, though he seldom uses it. I put one in with Bandit two weeks ago..he had started having shredded/bite marks on his tail...I was just cleaning his tank and felt the inside of each of the holes in the betta log, and they are really sharp and jagged! I can't believe how bad they are..I removed his, and will take Buddy's out now too...I'm not sure if I can grind them down. Anyone with these logs in their betta tanks should check theirs out too.