石が(いしが)不運にも(ふうんにも)イモリの頭に直接当たり、一瞬(いっしゅん)のうちに死んでしまった

Furthermore, one evening, 'I' discovered a single 'newt' resting on a stone in a roadside stream. With no malice, thinking 'I will startle that newt and drop it into the water,' 'I' threw a small stone near it. However, the stone unfortunately struck the newt's head directly. The newt died in an instant and stopped moving. At this completely unexpected, sudden 'death of the newt,' 'I' was struck by a fierce creepiness and pity.