I've had several hamsters and was wondering why they do a certain behavior. Sometimes my hamster will suddenly stop whatever it is doing and stay completely still until I move around or say something. After moving/saying something, my hamster will then continue doing whatever it was doing before it froze. I have also heard from other people that their hamsters do this. Is there a reason that hamsters do this?
This is actually a very common behavior for hamsters to show. Almost always, it is nothing to worry about. This could happen for a variety of reasons including if your hamster is listening for something, surprised, and/or scared.
When hamsters hear an unfamiliar sound, they may freeze to listen to it. They are probably trying to figure out if the sound is coming from anything important to them (ie: a predator). After a while, your hamster should stop freezing to the same sound because they become more familiar with that sound. Your hamster may also freeze from a sudden sound because they are surprised and/or scared. For example, if your hamster was munching some food, and you suddenly opened the door and walked in, the hamster may be startled and freeze. A hamster will likely be scared if they hear a really loud sound (hamsters have very sensitive hearing). If a hamster hears a loud dog barking or a door slamming, they will likely be scared and may freeze temporarily or try to hide depending on the hamster.
So, a hamster freezing (unless your hamster is constantly freezing, freezing for very long amounts of time, or not being responsive after freezing) is really nothing to worry about.
You can read more about this here.