Do you already have other offers for vet med? If you have another offer do not reapply just for the chance of getting into Cambridge.
For the interview:
Do as much science further reading as possible between now and October. Stock up on work experience- while you’re there be super inquisitive, take notes, ask how stuff works (try and familiarise yourself with what each bit of equipment they use does, common drugs and what they do- they won’t directly ask you about a specific drug but it’s useful to mention in questions, and treatments for common conditions you see). See if your school can set you up a mock interview.
The questions themselves (as I’m sure you know from your last interview) are not that hard just phrased in a way that makes you think about it to get to the answer. If you don’t know the answer to a question, think out loud! Tell them what you are doing to try and work out the answer. Don’t sit there in silence.
I got a Cambridge offer for vet med this year by doing this stuff (from Downing). You probably know you aren’t meant to reapply to the same college so choose another one, and good luck!