Mouse odd-ness

[marisa]

I have a ten gallon tank where I put some of my offspring to get larger for my bigger corns. I normally leave them there for quite some time.

Anyways right now the mice have been doing a weird thing. They are often seen standing up in the middle of the tank. On their hind legs. Sometimes I see one or two mice doing it, but other times its a group of them standing up on their hind legs together.

I would take a photo but they stop doing it and run off when they see me coming or when I open the cage.

What is this? None of my other mice do it, and these mice that are doing it are healthy, eating and growing. But its clearly odd behavior. Any ideas?

Marisa