I need a type of goo for an art project. Any ideas?

O.k. so i have a gl jar and I made a mermaid in it. I want to have a type of slime or goo in it so she can move around just a little bit (or a lot! I'm not picky right now lol) but is basically clear. So you can see her well and when I glue the jar shut it wont dry out so she can keep moving... any ideas as to what I can use????