The major mystery in Ariana Grande's 'Carpool Karaoke' episode

Firstly, this episode of Carpool Karaoke is up there with the best. The harmonies between her and James Corden are literally amazing. 

The segment when the two pop into a cafe is hilarious. 

BUT can someone please explain why Ariana has a bandaged up hand?! What happened! 

Aside from that, fantastic episode, just great.