Successful meetings create a safe environment for contribution; one that attendees feel engaged in and part of. Previous research has shown that meetings success depends not only on execution, but also on whether attendees feel psychologically safe. While this aspect is, to a great extent, partly observable through certain body cues during in-person meetings, they are often overlooked in virtual ones. To partly fix that, we developed Kairos-a system for multi-modal monitoring of virtual meetings that captures subtle body cues. We deployed it in 55 real-world corporate meetings and, upon six metrics for body cues, we built a model to predict a meeting's self-reported success, achieving an AUC as high as 79%. We found that certain body cues were more predictive of a meeting's success (defined as a linear combination of execution and psychological safety) than others (head movements, for example, were twice as predictive as hand movements), not least because they captured three typical meeting phases (its initiation, collective discussions, and turning points) whose presence (or absence) greatly mattered for success.