Duvet inserts usually can be put in the washing machine, but double-check the tags first. If it says “dry clean only” or something similar, then don’t wash it because you could ruin the duvet.
Our bum crack is medically referred to as the intergluteal cleft.
The crena is another formal term used for the cleavage of the buttocks. We have butt cracks mainly due to the preliminary muscles that sit inside the evolved pelvic bones.