  Explainable reinforcement learning (XRL) methods aim to help elucidate agent
policies and decision-making processes. The majority of XRL approaches focus on
local explanations, seeking to shed light on the reasons an agent acts the way
it does at a specific world state. While such explanations are both useful and
necessary, they typically do not portray the outcomes of the agent's selected
choice of action. In this work, we propose ``COViz'', a new local explanation
method that visually compares the outcome of an agent's chosen action to a
counterfactual one. In contrast to most local explanations that provide
state-limited observations of the agent's motivation, our method depicts
alternative trajectories the agent could have taken from the given state and
their outcomes. We evaluated the usefulness of COViz in supporting people's
understanding of agents' preferences and compare it with reward decomposition,
a local explanation method that describes an agent's expected utility for
different actions by decomposing it into meaningful reward types. Furthermore,
we examine the complementary benefits of integrating both methods. Our results
show that such integration significantly improved participants' performance.
