A firecracker converts chemical energy into sound.
Most any other sounds can be frightening or startling.
Firecrackers can be startling.
What can be startling?
[1] firecrackers
[2] an image
[3] Saltine crackers
[4] Wheat crackers
[5] an object
[6] sea urchins
[7] sameness
[8] hypothyroidism