In a recent study of the part of Sh'mini about Nadav and Avihu bringing aish zarah (alien fire), somebody vaguely recalled a midrash that the fire that killed them entered through their nostrils and burned them inside rather than them being engulfed in flames from outside as I'd always imagined the event. I found an article on the Chabad site that mentions this midrash and cites Tanchuma (nothing more specific). I tried searching Tanchuma (in English) on Sefaria but did not find this midrash. (I can work with a result in Hebrew but searching in Hebrew hasn't worked so well for me yet.)
Where can I find this midrash? I'd like to know what it says about what happened and also any conclusion it reaches about why it happened that way. (I have guesses about the latter but nothing I can support.)