If things go belly up, they have failed. Think of a dead fish ...

It means that something goes badly wrong.

It can also mean to step up, as to a bar -- the image is to put your belly next to something.

When a sail fills out because of wind blowing in it, the curved, concave part is called its 'belly'.

If you are sitting, sometimes your penis will stick straight up as it is flaccid. If it then begins to become erect, it will continue to move upwards towards your belly so that when you stand up it will remain at your belly.

there belly swells up and there ankles go redish

Snakes have the ability to go up stairs. They use the belly muscles to move and that is the same way that they will go up the stairs.