The two also perform two acapella duets of two of Demi's songs, "Stone Cold" and "Sorry Not Sorry," in which they proceed to fangirl like crazy over one another. It's really cute.
The whole chat (2) --
"Stone Cold" (3) --
"Sorry Not Sorry" (4) --
(This is something Tori is regularly doing. She's had Jessie J on in the past. I think she sings the songs of her guests every time. I only watched this one with Demi.)
Sources: All YouTube videos 1 | 2 | 3 | 4