[Nush]

My hammy bar chews whenever he wants to come out. He doesn't do it often, only the 3 to 4 times he wants to come out. I think they try it and see if you respond and once you go and check on them, they learn that they can get you to do what they want!

It may well be that when he was in the aquarium, he did want to come out but didn't know how to tell you.

Obviously, like me, if you keep going to see him every time he bar chews it'll only reinforce his behaviour. If you ignore the bar chewing, no matter how loud he is, he'll stop. Because my hammy only does it a few times, I haven't discouraged him. I got his teeth checked by the vet a few times now and he said his teeth are well aligned so the bar chewing is not excessive enough to make an impact.

My Syrian tells me he wants to come out when he sits by his door. He's quite a patient guy, bless him. The way to train him is to wait for him to do an action e.g. sit on a ledge then go and see him every time. So that he learns every time he sits in a particular place you will likely take him out.