(Excerpt from the Slam Course with Grizz and Caitlin)

grizz: the south hand is huge, with only 2 losers and great shape, so he opens 2C
grizz: responder has 10 losers and a so-so suit, so 2D is the correct response here
grizz: it is not good enough for 2S
grizz: but since the pair plays 2H as a supernegative, the 2D bid is constructive
grizz: ok everybody, what should N bid?
grizz: hint: the Principle of Fast Arrival applies here
Student 5: 4 sp
grizz: righto
grizz: no extras, no interest in slam, nothing to cue
grizz: but S has a better than average hand here!
grizz: lol  you might have noticed that already
Student 4: just 2 losers
grizz: void in C, no losers in H, no probable losers in D
grizz: and with the known S fit, the only possible losers are in trumps
grizz: so how does S go about finding out about possible trump losers?
Student 6: 5s
grizz: 5NT is a Grand Slam Force in any suit
grizz: not just in S, any suit
grizz: it says: "partner, we have 6 in the bag.  if you have 2 of the top 3 honors, bid 7"
grizz: and N, looking with incredulity at his 10 loser hand, sees the SKQ, gulps and bids 7S
grizz: tada!
grizz: 25 hcp grand slam, and it's cold
grizz: if partner has only 0 or 1 top honor, he must sign off in 6
Student 4: can south also bid 5 C Exclusion Blackwood?
grizz: 5C would not have been a jump, so it would have been a cue, or somehow ambiguous
grizz: at any rate, 5NT is crystal clear
grizz: and when your only question is about trump losers, that's the question to ask
grizz: any other questions?
grizz: one last hand then
Student 3: isn't it risky to commit to 6 missing KQ?
grizz: some risk, yes
Student 7: what about 4NT?
grizz: if S asks 4NT and N shows 1 control, is it the SK or the CA?
grizz: one is useful, the other not a bit
Student 7: oh ok, ty
grizz: might only be a 9 card fit
grizz: but don't you think the field will be in 6 here?
Student 3: I'm not sure if I would be brave enough  :)
grizz: :)
Caitlin: but the South hand is only a 2 loser hand
Student 3: yes it's true, and partner did promise some values with the 2D
grizz: yes - 2H was supernegative, and pd did not use it
grizz: so south must have at least a K somewhere
grizz: so when your only questions are about the trump suit, 5NT is a great gadget to have in your bidding toolbox
Student 2: how to get hands like these in real life ?
Student 5: lol
grizz: they don't come along very often    lol
grizz: but when they do, you are prepared!
Student 4: play 1000 hands a month!
Student 2: omg
grizz: ok gang, that's all for today