  We investigate a tantalizing symmetry on Catalan objects. In terms of Dyck
paths, this symmetry is interpreted in the following way: if $w_{n,k,m}$ is the
number of Dyck paths of semilength $n$ with $k$ occurrences of $UD$ and $m$
occurrences of $UUD$, then $w_{2k+1,k,m}=w_{2k+1,k,k+1-m}$. We give two proofs
of this symmetry: an algebraic proof using generating functions, and a
combinatorial proof which makes heavy use of the cycle lemma and an alternate
interpretation of the numbers $w_{n,k,m}$ using plane trees. In particular, our
combinatorial proof expresses the numbers $w_{2k+1,k,m}$ in terms of Narayana
numbers, and we generalize this to a relationship between the numbers
$w_{n,k,m}$ and a family of generalized Narayana numbers due to Callan. Some
further generalizations and applications of our combinatorial proofs are
explored. Finally, we investigate properties of the polynomials $W_{n,k}(t)=
\sum_{m=0}^k w_{n,k,m} t^m$, including real-rootedness, $\gamma$-positivity,
and a symmetric decomposition.
