Some people use a needle but a slightly bigger hole does a better job. My neighbor used a small scalpel on his tom after a needle failed to keep it drained long enough. Even a single edge razor blade could be used if done so carefully.So what does one pierce it with? This seems like an Incredible Doctor Pol moment (from the Nat Geo Wild TV channel); he's always lancing parts of animals, either to release air (for bloat) or pus (from a swollen mass of infection).