Seeing that they were close to done, professor Slughorn visited their station as well, examining the potion and then deciding that it was probably safe enough to drink. Ambrose took a cup and served himself some, looking at it skeptically. That was one of the benefits of partnering with Ridgebit, at least - he didn't expect there would be all that significant a difference once he drink it.
"Bottoms up, I suppose," he said, and took a drink.