Change management difficulties

Hello, one statement in the change management lecture resonated quite well with me and referred to the verbal and active resistance which speaks up and can be easily identified – the statement was about using that “energy” and convert it into positive energy. But what about the non-verbal, passive resistance (e.g. increased sick days etc.) – I find it incredibly hard to identify that (and determine if related to the M&A) and to find the right measures to combat it – what are your observations?