This is a prop plague doctor syringe. The plunger can move give the appearance that the fluid is being extracted and injected. The needle head retracts to make it look like the needle is being injected. I've included a drawing and a few videos showing how it all comes together.
Check out the gifs below for assembly instructions. I'd dry fit all the components together to make sure you don't have in hangup with the parts before gluing. Some parts have a tight fight, so you might want to use a chamfer tool on the OD and ID's.
The author marked this model as their own original creation.