Thank you very much! I'm glad you like my little game/prototype :)
It's quite easy to achieve this effect. The only thing that took a lot of time was tweaking the settings to make it feel right. A tongue consists of a lot of short segments which are connected via 2D joint. A line renderer component draws tongue from each coordinate of each segment (there is also a varying width of each point). I think the wobbliness comes from the tongue being always pulled into the frog and pulled by a mouse.