First it says
כָּל הַנֹּגֵעַ בָּהָר מוֹת יוּמָת
Then a Posuk later:
אִם בְּהֵמָה אִם אִישׁ לֹא יִחְיֶה
Why is there a double death warning?
The Daas Zekeinim explains that someone who touched the mountain got killed through stoning. The second warning is that those that stone the one who touched the mountain should do it from afar.