Why is "nodev" in /etc/fstab so important? How can character devices be used for hacking?

I am learning about linux security and struggling to understand why a USB stick with a character device on it is potentially dangerous.

If I have a USB stick with a bash executable that has setuid root on it, the danger is obvious: Anybody with such a USB stick can gain root privileges on my computer if I have an entry like

/dev/sdb1 /media/usbstick auto defaults 0 0

in my /etc/fstab because defaults includes suid.

But what about character devices? How can I use a character device to gain root privileges or break stuff if a USB stick with a character device on it gets mounted with dev or defaults?