I looked and couldn't find another post like this, but I may have missed it.
Very often, when a play walks tight up against a wall, they protrude through the other side for moments. They are not glitching entirely through, the wall still blocks them from moving.
While its nice for me, because on multiple occasions I've seen people before they come into the house I'm in, or if they are on the other side of a wall, its pretty unfair to everyone.
(I'm not sure if you can shoot them while they are glitched through)