  If $X=(V(X),E(X))$ and $Y=(V(Y),E(Y))$ are $n$-vertex graphs, then their
friends-and-strangers graph $\mathsf{FS}(X,Y)$ is the graph whose vertices are
the bijections from $V(X)$ to $V(Y)$ in which two bijections $\sigma$ and
$\sigma'$ are adjacent if and only if there is an edge $\{a,b\}\in E(X)$ such
that $\{\sigma(a),\sigma(b)\}\in E(Y)$ and $\sigma'=\sigma\circ (a\,\,b)$,
where $(a\,\,b)$ is the permutation of $V(X)$ that swaps $a$ and $b$. We prove
general theorems that provide necessary and/or sufficient conditions for
$\mathsf{FS}(X,Y)$ to be connected. As a corollary, we obtain a complete
characterization of the graphs $Y$ such that
$\mathsf{FS}(\mathsf{Dand}_{k,n},Y)$ is connected, where $\mathsf{Dand}_{k,n}$
is a dandelion graph; this substantially generalizes a theorem of the first
author and Kravitz in the case $k=3$. For specific choices of $Y$, we
characterize the spider graphs $X$ such that $\mathsf{FS}(X,Y)$ is connected.
In a different vein, we study the cycle spaces of friends-and-strangers graphs.
Naatz proved that if $X$ is a path graph, then the cycle space of
$\mathsf{FS}(X,Y)$ is spanned by $4$-cycles and $6$-cycles; we show that the
same statement holds when $X$ is a cycle and $Y$ has domination number at least
$3$. When $X$ is a cycle and $Y$ has domination number at least $2$, our proof
sheds light on how walks in $\mathsf{FS}(X,Y)$ behave under certain Coxeter
moves.
