In the Moldvay basic booklet, the second sentence of page 13 says "All characters and monsters capable of speech speak the language of their alignment (Lawful, Neutral, or Chaotic)". Somehow (probably owing to the quantity of wine I had drunk), I managed to forget the three bold words in the previous sentence. In my defense, they are not bolded in the actual book, possibly because Tom Moldvay didn't suspect anyone would be dumb enough to screw this up, but then again, Tom Moldvay never had me as a player.
Because I forgot these three words, I allowed Smallie Biggs (the dwarf in our campaign) to use alignment language to speak with an orangutan. I guess the idea of a drunken dwarf trying to use some bizarre combination of gesticulation and cant to avoid combat with an ape entertained me enough to let it fly. I figure no harm was done, and it's a funny moment in the ongoing story of the campaign.
However, Smallie has since used alignment language to speak to a cobra and a pair of baboons (there's a bit of a Johnny Quest theme to my home-brew encounter tables). I considered disallowing this, but only briefly, because that original encounter with the orangutan had become a memorable part of the established canon.
Sometimes mistakes lead to good things. In this case, a mistake led to a game world in which all animals can talk and be understood- as long as you share the same cosmic world view, i.e. alignment. Some may see this as a bad, silly, or outright stupid thing, but I'm happy it happened. It opens the setting to ideas I might never have other wise considered, and perhaps more importantly, it provides more opportunities for role playing. I think negotiating with a Grizzly Bear could make for a more entertaining game situation than simply drawing swords and fighting one. And anyway, if the PCs fuck up the negotiation they'll still get a chance to be mutilated, so it's a win/win.
The concept of talking animals has been around for about as long as humans have been telling stories. If it's good enough for Bullfinch, it's good enough for me.
*another word I only know because of Gygax.