Sounds like there a variation of drinks, some pink, some clear. Nadia goes in 1st, Jason & Stu are going last as they think they're more likely to drink them than the others.
Shell suggests sensibly that they should go first if they're just going to drink what they can.
The point is BB can't give them anything that is going to do them harm so take a deep breath, down it, come out and have a long drink to take the taste away.