During Yusuf's recruiting for the Inception he's about to show Cobb and the others how his special sedatives work in practice. But right before showing them he hesitates for a short moment:
Yusuf: This I think is a good place to start, I use it every day.
Cobb: What for?
Yusuf: Here, I'll show you...(hesitating)...Perhaps you will not want to see?
Cobb: After you.
It might be that I'm making more out of this than there is to it, but I couldn't wrap my head around why he hesitates, especially since from saying "Perhaps you will not want to see?" it doesn't seem to be his own reservations for a deal with Cobb that are in the way, but Cobb's possible reluctance to look any further, which I don't think Cobb has given any indication for. So why did Yusuf hesitate to shown them his sedative in practice (or rather imply that Cobb would hesitate to see it)?