When a snake flicks its tongue, it is gathering odor particles for transfer to two fluid-filled sacs at the roof of the mouth -- Jacobson's organs -- that lead to a second, smaller olfactory chamber. The tongue is used only to assist in this process; snakes do not have a sense of taste.
A eukaryote is a type of cell (or unicellular organism) that possesses a nucleus and membrane-bound organelles, in contrast to prokaryotes (bacteria and archaea) which don't. Eukaryote means good/true nut/kernel in Greek, referring to the nucleus, while prokaryote means before nut/kernel.
Honestly, we could come up with reasons all day, but the simple fact is that eukaryotic cells are up first. C'est la vie. Eukaryotic Cell Structure and Function A cell is defined as eukaryotic if it has a membrane-bound nucleus. Any organism composed of eukaryotic cells is also considered a eukaryotic organism. Case in point: you. Oh, and all other people, too. Biologists do not know of any organism that is composed of both eukaryotic and prokaryotic cells.