Meet “Bookie”.
Bookie is a not very special soft book. Unless you are Thing 4, and Bookie is the your favorite comfort object.
She sleeps with it every night, putting it under her head as a pillow. She carries it everywhere. When she is upset, she asks (screams) for Bookie and it calms her down.
Thing 2 had his favorites. And Thing 4 has Bookie.