# he foams at the mouth

A convulsion, or seizure, can cause a person to have trouble breathing or swallowing. This causes white foam to come out of the mouth. If your language has a way to describe that, you could use it. AT: "bubbles come out of his mouth"

# he becomes rigid

"he becomes stiff" or "his body becomes rigid"

# they could not

This refers to the disciples not being about to drive the spirit out of the boy. AT: "they could not drive it out of him" (See: [[rc://en/ta/man/translate/figs-ellipsis]])