LOl, no way at all that a YFW will kill a cat lol, cats are quite tolerant to snake bites and they will need more than a bit from a YFW to knock it over.
unless the cat chokes on it......
They can have worse effects on humans than numbness though, major swelling, pain, nausea ect can be the end result, size of the snake has alot to do with it and whilst the average whip is around 40 cm or so they can double that size and large whips should be treated with alot more respect