Final answer:
The statement 'My heart beats when I behold a rainbow in the sky' is a metaphorical expression.
Step-by-step explanation:
Based on the provided information, the statement 'My heart beats when I behold a rainbow in the sky' is most likely a metaphorical expression. It is not a scientific observation as it does not describe a factual or observable phenomenon.
It is also not a medical condition or emotional response in the traditional sense. The statement is using figurative language to convey a feeling of excitement or joy associated with seeing a rainbow.