Premise:
"'Can't go that way.'"
Hypothesis: Can't go down that road or you will die!

it is not possible to tell

Premise:
"must be explained and the reference toxicant test must be immediately repeated."
Hypothesis: The reference toxicant test must be repeated immediately.

yes

Premise:
"they must think Americans are just really terrible if they watch this"
Hypothesis: Americans are perceived to be terrible.
yes