In Killer Bunnies do you replace a very special card when played?
The rules state that you can play a Very Special card from your hand at any time, even when it's not your go.

The rules also state (order of operations) that at the end of your go you should have 5 cards in your hand and 2 in the run. So you should take a card when you play a Very Special card, although it's not completely clear whether you should do so immediately or wait until the end of your go to do so. Unless you happen to pick up another Very Special card or a Play Immediately card I don't think the timing actually makes any difference.

Anyway, I've always played that you take a replacement card immediately when you play a Very Special card from your hand, it seems the most sensible approach.