それが燃えているのを知ってびっくりした。

that (indicating an item or person near the listener, the action of the listener, or something on their mind); it; that time; then; there (indicating a place near the listener); you

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to burn; to get fired up

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to be aware of; to know; to be conscious of; to cognize; to cognise; to notice; to feel; to understand; to comprehend; to grasp; to remember; to be acquainted with (a procedure); to experience; to go through; to learn; to be acquainted with (a person); to get to know; to concern

to be surprised; to be amazed; to be frightened; to be astonished; to get startled; to jump; surprise (e.g. surprise party)