Once I saw an old tree with a knot bulging in the bark, so I tried to hack it off with an axe, to no avail.
The bark had been removed, but no wood was shown, only a tumor-like growth, caused by a careless insect no doubt, that realized it would not be a suitable home.
I showed my father the growth, hoping he could save it, cut out the bad, so it would no longer plague the oak, so it could be normal again.