Tiny slug? Would love an id.

[justaDutchguy]

I just found this tine green slug like thing, it contracts every few seconds, the way a cat does when it has to vomit. It's about 1mm long and moved slow. I tried making a pic but it's quite blurry.
It's the little green "slime" in the center of the pic.

 

[Eckolancer]

Can't really make it out.

 

[Reefing Madness]

Can't see it