Let's Make Robots!

fish robot help flopping

'Flopping fish'

First of all I'm art student, therefore (as you may expect) I know nothing where electronics is
concerned. I have come onto here wondering if you could guide/ recommend/ give any advice.

I'm currently starting a new art project as part of my university course.
What I require is a series mechanism/ piece of electronics which could fit inside a
model of a fish (hand size) and make it flop without assistance.