That Rule in B/X I Missed...

I'm sure there are a couple of more I could find, but this one, this one I can testify I never internalized, or had it come up in play, hmmm. Anyways, it is a good optional rule and I am writing it down here so now another piece of B/X lore is firmly cemented into the space in my brain labeled "If it isn't about ttrpg's I'm not interested". 

It is on page B25 and it goes like this; "ATTACKS ON 'UNHITTABLE' CREATURES (OPTION): Some creatures can be hit only by silvered or magic weapons. The DM may want to allow two other kinds of attacks to hit such creatures. First, attacks by other 'unhittable' creatures may be allowed (for example, a lycanthrope could attack a wight). Second, attacks by monsters with more than four hit dice may be allowed (an owlbear could attack a wererat)."

Seems reasonable to me. I like it. I also like being reminded the clarity of Tom's language usage in writing the Basic Rules. Many rules can be written with some running of the mouth by an author. Tom Moldvay commits none of these sins. I still use this book as a style guide when considering the words I'm using when writing rules.