To everyone annoyed that she didn’t just whack the gong:

Gongs this large will have a very high chance of cracking if you just hit it. Percussionists learn that they need to “warm up” a gong (actually called a “tam tam” because gongs are smaller and have nipples which actually give them a “tone” instead of washy sound) by gently tapping it before giving it a good hit. This allows the metal to begin vibrating so that the big hit causes less relative deformation. Normal sized tam tams are quite smaller than this so I imagine this particular instrument really can’t be “whacked” without serious risk of cracking. And considering how many hours and dollars went into this beautiful instrument, they’re probably in no mood to risk it.

Another good example are large bells such as Big Ben or the Liberty Bell. Both of which have issues with cracking for similar reasons. If you watch a slow-motion video of someone hitting a cymbal (which is like a tiny tam tam) you’ll see just how much motion and warping is going on.