この動物たちは花火の音にびっくりした。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

fireworks

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

sound; noise; report; note; fame; Chinese-derived character reading

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

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