The sign language equivalent of tongue twisters are called 'finger fumblers.'
English isn’t the only language with phrases created for the sole purpose of tongue tying the speaker. There are tongue twisters in Chinese, Arabic, Hindi, Swahili, etc. Even sign language has its own version of the phenomenon called finger fumblers. “Good blood, bad blood” is an example of one such finger fumbler.
Sure you can say it just fine with your mouth, but it’s quite difficult with your fingers. In fact, parents and family of deaf children often use finger fumblers to help them practice their sign language. In fact, practicing tongue twisters have been proven to increase proficiency in just about any language. Still not satisfied? Read the source!