Aw, that's a shame. I think it was clearer in the re-edited version (which is on disc two of the DVD, if you have it). And it's longer in the novelisation! It's the bit where the haemovores start properly breaking through and the Doctor goes very still, if you want to go back and look for it.

I think lost_spook is right about the rain! The weather was certainly really weird during the location filming, as far as I can tell.

They are... unfortunate. ;) I think the extras said that animatronics were a fairly new thing at the time, and someone on the production team saw some really good animatronic dogs and thought "hurray, that'll be better than trying to use live cats"... not realising that animatronic cats don't work nearly so well!