Unless this is a recurring dream, I really don't think this has any meaning. You could have had those elements on your mind the day before that and it decided to pop up in your dreams. But either way, I'll give you my interpretation:

Considering you had a bad feeling of the cat (being you thought it was a zombie) even though it showed no signs, it could be that something is concealed in some way in waking life. Often times in dreams when something has a violent/scary behavior, it's likely some negative representation in your life. So if you have some not so obvious bad event or feeling in waking life, this might be the case.

Now, whether or not this negative occurrence was in the past or not, basically your hostile tendencies towards the cat may (have) signify (ed) that you must (or have) cast aside those bad things. When the cat disappeared, you were angry that he killed it when he could have done it earlier. Your subconscious may be telling you that either you or a 3rd party could easily help your situation.

If it matches your current situation in any way, then this might be the correct interpretation. Sweet dreams..