Brian,
Note: Some manuscripts end the book with 16:8; while others include 9-20 immediately after verse 8. A few manuscripts insert additional material after v. 14; one Latin manuscript adds after verse 8 the following: But they reported briefly to Peter and those with him all that they had been told. And after this, Jesus himself sent out by means of them, from east to west, the sacred and imperishable proclamation of eternal salvation. Other manuscripts include this same wording after verse 8, and then continue with verses 9-20. TLSB, p. 1697
Mark's abrubt ending: As the ESV text note for 16:9-20 shows, these verses do not appear in a number of early Greek manuscripts. This likely means they were not part of Mark's original composition, which may have used a "suspended" ending that left readers wanting to learn more about Jesus and His deisciples. The longer ending was perhaps added later to satisfy people's interests. TLSB. p. 1653.
As to verse 18 (snakes), the note states: God promises to protect us, but we should not tempt or test Him. Cf. Acts 28:3.....
Now, just buy the book so you can read the rest for yourself.