  Given a 3-hypergraph $H$, a subset $M$ of $V(H)$ is a module of $H$ if for
each $e\in E(H)$ such that $e\cap M\neq\emptyset$ and $e\setminus
M\neq\emptyset$, there exists $m\in M$ such that $e\cap M=\{m\}$ and for every
$n\in M$, we have $(e\setminus\{m\})\cup\{n\}\in E(H)$. For example,
$\emptyset$, $V(H)$ and $\{v\}$, where $v\in V(H)$, are modules of $H$, called
trivial. A 3-hypergraph is prime if all its modules are trivial. Furthermore, a
prime 3-hypergraph is critical if all its induced subhypergraphs, obtained by
removing one vertex, are not prime. We characterize the critical 3-hypergraphs.
