What chemical knowledge is there in the poem?

Du Fu was a famous poet in the Tang Dynasty, leaving us many immortal poems that have been passed down through the ages. In a poem, he described a very confusing and annoying thing:

The guests came from there and gave me a spring guest bead.

There are words hidden in the beads, so you can't tell a book apart.

In order to meet the needs of the public, I kept silent for a long time.

Broaden your horizons into blood, and decline leads to stagnation.

The main idea of this poem is that a guest is from the south. He gave the poet a pearl with a design or handwriting on it. The poet kept it in a box. After a long time, he opened the box, only to find that the pearl had disappeared, leaving only some red liquid. Can you explain this phenomenon for Du Fu? As we all know, pearls are made up of secreted substances produced by the stimulation of the mantle of pearl oyster. Its main components are calcium carbonate and a small amount of organic matter. Calcium carbonate is insoluble in water, but can be converted into acid salt and dissolved under acidic conditions;

The house where Du Fu lives is leaking and damp, and the bamboo box has no moisture-proof performance. When pearls meet carbon dioxide gas in water and air, they change chemically and become red liquid. Du Fu didn't know these chemical knowledge at that time, so he was puzzled.