The grin is tipping James off, but he isn't quite sure of what Raju's doing until the next set of turns. Once they're two turns in he's confident enough to call Raju out on it, laughing a little.

"Daring, to add unexpected turns. You must have little fear for your feet." Between the general risk of getting stepped on during a dance, James is also somewhat drunk, which only increases the risk. But he's clearly amused by this little change of pace, and honestly not too bothered by having a little break from the more strenuous part of the dance; he may have overestimated his strength a bit, but is absolutely unwilling to admit such a thing.