  Erd\H{o}s, F\"uredi, Rothschild and S\'os initiated a study of classes of
graphs that forbid every induced subgraph on a given number $m$ of vertices and
number $f$ of edges. Extending their notation to $r$-graphs, we write $(n,e)
\to_r (m,f)$ if every $r$-graph $G$ on $n$ vertices with $e$ edges has an
induced subgraph on $m$ vertices and $f$ edges. The \emph{forcing density} of a
pair $(m,f)$ is $$ \sigma_r(m,f) =\left. \limsup\limits_{n \to \infty}
\frac{|\{e : (n,e) \to_r (m,f)\}|}{\binom{n}{r}} \right. .$$ In the graph
setting it is known that there are infinitely many pairs $(m, f)$ with positive
forcing density. Weber asked if there is a pair of positive forcing density for
$r\geq 3$ apart from the trivial ones $(m, 0)$ and $(m, \binom{m}{r})$.
Answering her question, we show that $(6,10)$ is such a pair for $r=3$ and
conjecture that it is the unique such pair. Further, we find necessary
conditions for a pair to have positive forcing density, supporting this
conjecture.
