  For a dynamical system $(X,f)$, $X$ being a compact metric space with metric
$d$ and $f$ being a continuous map $X\to X$, a set $S\subseteq X$ is scrambled
if every pair $(x,y)$ of distinct points in $S$ is scrambled, i.e.,
$\liminf_{n\to+\infty}d(f^n(x),f^n(y))=0$ and
$\limsup_{n\to+\infty}d(f^n(x),f^n(y))>0$. The system $(X,f)$ is Li-Yorke
chaotic if it has an uncountable scrambled set. It is known that, for interval
and circle maps, the existence of a scrambled pair implies Li-Yorke chaos, in
fact the existence of a Cantor scrambled set. We prove that the same result
holds for graph maps. We further show that on compact countable metric spaces
one scrambled pair implies the existence of an infinite scrambled set.
