Loving these reactions! The shorter dance at 7:40 is actually apart of a group dance. They are called the Wiggle Crew from 2018. You should definitely react to that and the BTS on Alexander Chung's channel. It will introduce you to alot of great dancers that sean and kaycee also work with.
The Sean and Kaycee channel has a bunch of cooking and food challenges you may like hehe Telepathy Pizza Making, One Color Cook Off, an blindfold ice cream tasting and a popcorn ranking, a recent one is "Sean Teaches Kaycee How To Cook" :D
The dance where you felt like they were a lot more serious is kinda supposed to be like that as it was a class for professional dancers who aspire to pursue dance as a career, the class was by Galen Hooks (an amazing choreographer) who taught them not only the choreo but how to approach it depending on what role they were given as if they were doing a job, in this case Kaycee was the artist and Sean the backup dancer. Also the floor in that studio looks like that as it is specially made so dancers can dance and do crazy acro without hurting themselves. As always great reaction!!
The one that was really really short is from the Wiggle Crew 2018, they were part of a crew in an event in Boston, highly recommend!! There are two performances "Group" and "Change" And your favorite one is called "Brother", one of my favs of all time too :) Loved your reaction as always!!
Love you dude. You're awesome and encouraging. Dance is like singing for the body. It's actually not that hard to memorize the choreography when you repeat it multiple times within a few hours and then just perform it in class. Also, the movements fit the flow of the music. Like there are notes and certain pitches to a song and the movement usually matches the notes. I feel like it's almost like short term memory because when I danced I would usually forget choreography the next day if I knew I was only doing the choreography for that particular class and not performing it again in a competition or show.