Anyone who has been nervous around a crush will recognise the feeling here. The speaker imagines the moment of seeing someone they care about, and the fluttery, jittery sensation in the stomach gets pushed much further than usual. These aren't gentle butterflies. They are "going to war," which turns a sweet nervousness into something loud, forceful and a little out of control.
The short, clipped lines help. The pause before "they are / unstoppable" works like a drumbeat, a small announcement that the speaker has no say in what their body does. There's a mix of excitement and helplessness in that. The word "when" matters too: the speaker is certain this meeting will happen, and already feels the rush before it arrives. The mood is playful and breathless, with a hint of vulnerability underneath. Attraction here feels less like a quiet glow and more like a battle the heart can't help but join.