To be shtummer means to not make any sound or to not talk.
Being shtummer can be a good thing when you need to listen or when you are playing a game. But sometimes, being shtummer can make people feel sad or worried.
Examples:
The room was shtummer when everyone was sleeping.
She was shtummer during the game of hide and seek.
He felt shtummer after losing his favorite toy.
The cat is shtummer when it's hunting.
The forest was shtummer, and I felt a little scared.
The library is always shtummer because people are reading.