What does Nitrous oxide smell like?

Nothing? At least when I had it in hospital a long time ago it smelt like nothing.

It smells kind of sweet, from what I recall (at the dentist obv)

It doesn't have an odour. You can get it at sex shops, don't ask me why you don't want to know. You need to buy a cracker separate, to be able to fill balloons with it. It goes great with psychadelics and green bud by the way.