She had great control of her temper; bitingdown hard, she said nothing.
她很能控制自己的脾气,所以竭力忍着,一声不吭。
2
They have a little enzyme that when they are bitingdown in you it gets released in your blood and generally you bleed for quite a bit - and your health is optimized.
Bitingdown on a hunk of metal is more likely something someone might have done during the gold Rush to test whether the shiny golden rock they just panned for was actually pyrite or fool's gold.