There are many sayings and metaphors about flirting, which one could be found in a machine shop?
Options:
- feelings
- sexual excitement
- sparks fly
- problems
- unwanted pregnancy
Please answer and provide answer explanation.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Sparks fly in flirting means having a spark between two people. A machine shop has various machines that can have spark fly. The final answer: sparks fly.