Give blood from the trail elbow, not the hand
When golfers work on the "giving blood" trail-arm setup feel, the speaker often sees them slide the right hand underneath the club, which changes the grip. He notes that the wrist and the elbow are independent of one another, so the giving-blood feel should come from externally rotating the trail elbow; the right hand can then go on top of the grip.
Channel: PorzakGolf
Watch official source at 5:15Why this context matters
"Giving blood" is their setup cue for externally rotating the trail arm.