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.
The nucleus is an organelle that is surrounded by a double membrane called the nuclear envelope. The nuclear envelope separates the contents of the nucleus from the rest of the cell. Eukaryotic cells also have a cell membrane (plasma membrane), cytoplasm, cytoskeleton, and various cellular organelles. Animals, plants, fungi, and protists are examples of eukaryotic organisms. Animal and plant cells contain many of the same kinds or organelles.