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.
A eukaryotic cell is a cell that contains a membrane-bound nucleus. The nucleus is the control center of the cell, and it is sometimes referred to as the brain as it dictates how the cell grows, reproduces and functions. Information needed to carry out these activities is contained in long, stringy molecules of deoxyribonucleic acid, or DNA.