A handshake from a stranger made Nasrallah, traceable to Israelis; the man smeared him with the substance and then disappeared allowing Israel to track him
It would have to have been a highly waterproof substance. Muslims wash their hands before prayer five times a day. This is a cover story to distract attention from an Israeli mole at the heart of Hezbollah.
They are citing an Arabic report from IDF sources https://www.youtube.com/watch?v=90kkHdIFfzg
So the idea is locating him before going underground, his last 'visible' location before the signal disapeared.
