I've never seen cork rounds that small (narrow) but anything that your snake might get it's body stuck in could be a problem. They might fit thru before a meal, but not afterwards, for example...and their scales can catch & not allow them to back out, or if they can, it's only with severe injuries. Cork rounds also have an uneven texture that might complicate a snake being able to slide on thru. Whether natural or artificial "furnishings", just make sure there are no holes that your snake might get stick in...and pay attention as they grow larger. In your yard outside, snakes can get stuck & die in bird netting, chicken wire or even chain link (for larger snakes). You probably did the right thing by separating your cork round. You can also take an exacto knife & split them in half, into two equal tunnels.