Awaken and animals with HD: 1/2d8

[Darkness]

Among other effects, awaken adds 2 HD to a target animal.

What happens if the animal in question normally has only 1/2 HD? A cat, for example.
I think it wouldn't end up with 2 1/2 HD - that'd be weird (but not impossible, I suppose). Would it have just 2 HD, or...?

 

[andargor]

I can't a reference for that case, but it would be similar to adding class levels (in this case monster class levels, the first of which replaces the 1/2 HD). So your awakened cat would have 2 HD.

Andargor