There was a screech in the air and that was where Tony headed, rather than the muffled thumps of explosives and the other things. This was a battlefield of limited vision, of thick ground growth and moisture; he was not entirely surprised, with Parael on his back, when they stepped into chest-high water, and Tony kept going, with Parael held above the waterline so he wouldn't drown as they waded through. Water like this was safer, relatively speaking, though there was the danger of leeches and other things in the water.

He knew that haste was dangerous -- to crash around in the bush was to bring the attention of whatever was lurking in it. And so even though there was a fear-driven wish to rush toward, he held himself, tremblingly, as he moved forward deliberately, clambering onto dry(-er) land and then back into boggy swamp. There was one advantage, in a sense, to this. He wasn't laden down like he was as an infantryman in this crap. Moving through it in the throes of his first change after a disastrous firebase action that put his company under siege and overrun, even hit with friendly fire from artillery at Dong Tam, didn't give him much in the way of memories besides a surrealistic blur of animal instinct and pain, hunger and rage. It was his first change out here, and he didn't want to repeat the experience. His animal nature, which he closely reigned in ever since, went wild out here. 

That was why he was trembling. 

And then the rounds started to land, creeping up behind them, huge blasts that landed with a plume of dirt, water, smoke and fire, leveling the trees; not just one hit of artillery, which could shake the entire world if one was close enough, but a creeping barrage of 155mm rounds, hitting one after the other and moving up in their direction.

Now he ran, now he sprinted, heedless of the traps, while his eyes sought some sort of cover, some place to cower from the awesome and impossible firepower of field artillery.

This is what made him snap the first time.