How do I get the vase?

Try picking up the vase to see what will happen.

I bet there's a sensor under the vase that lets tells the laser to shoot.

It probably goes off when it detects a change in weight.

So all you need to do is find something that weighs as much as the vase.

Did you see that bottle floating in the water?

By itself, it probably isn't heavy enough, but you can take care of that
problem.  After all, you have plenty of "weights" around the tower.

Try filling the bottle with some water.