Hexagram 51 is the doubled thunder trigram, and it contains something rare in an ancient text: a written-out noise.
The judgement describes the shock coming, and then, in Wilhelm's rendering, laughing words, ha, ha. The Chinese is onomatopoeic, representing either laughter or the sound of the thunder itself, and translators handle it very differently. Legge renders the passage more soberly. The effect in Wilhelm is startling and slightly comic, and it is a fair representation of something genuinely odd in the original.
The judgement continues: the shock terrifies for a hundred miles, and he does not let fall the sacrificial spoon and chalice. That image, a person holding a ritual vessel steady through a thunderclap that frightens everyone within a hundred miles, is the hexagram's whole argument, and it is one of the most efficient pieces of writing in the book.
The line texts follow the shock through its consequences: fear leading to good fortune, danger with a loss of treasure that will be recovered in seven days without pursuit, shock that comes and goes, shock that ends in the mire, shock that goes back and forth with nothing lost but work to be done, and finally shock that brings ruin, with terrified glances, where going forward brings misfortune but the trouble reaches only the neighbour and not oneself.
Zhen is variously translated as The Arousing, Shock, Thunder and Quake. Wilhelm's choice of The Arousing pushes the figure towards initiative and away from alarm, which is defensible from the trigram commentary and rather less so from the line texts, where the dominant note is fright.