Does this mouse have any chance of staying calm in this situation? No way! But we do, with practice.
This enormous task is basically what you have to accomplish when it comes to dealing with your emotional reactivity (aka suffering/stress). Your mammal mind will be yelling at you, taking over your mind, in fact – cutting off your thinking/monkey and tensing-up your body/reptile. This happens instantly, especially when a deep, core reaction is triggered. Any hesitation and that mouse is done for. But your stressful situations are probably not quite as immediately life and death.
How can we possibly find equanimity in this situation? It's the human and reptile minds, working together, which will eventually allow you to stand firm in the face of an emotional hijack. You need awareness and then expressed acceptance. You are going to deliberately shift your body and breath into a (strong and soft) posture that's the opposite of reactivity (tension), and deliberately override your emotional signals.
Notice when you're reacting. (Noticing means that you're present and already accepting, to a degree.) Then physically accept the situation (and your body sensations) with a deliberate, opening, 4-part breath.