The hands and knees are synecdoches for the people themselves. Alternate translation: "Everyone will be so terrified that they will be unable to work and their knees will become weak so that they cannot stand" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
Another possible translation is, "every knee will flow with water," a euphemism for all the people losing control of their bladders because they are so frightened. (See: [[rc://en/ta/man/translate/figs-euphemism]])
# knee ... weak as water
Water cannot stand up, and the people's knees will be so weak that the people are unable to stand on their legs. (See: [[rc://en/ta/man/translate/figs-simile]])