"Bet" in the beginning of the sentence

Question

Bet it was a quick death, though. In this sentence, there is no noun before "Bet". Does it refer to "you" or "I"?

Answer 1

It refers to "I", always.

This omission is a practice you find with other verbs, in particular "tell" in the past tense; it is informal.

• Told you they wouldn't come. (ref.)