The title says it all...almost.
I was preparing a warm (90-100F) mixture of tap water, EV olive oil, and leaf lard (each about 50-60g). At first, the oil and water were added and brought to said temperature. Then, I added the leaf lard from a bag, squeezed out the end - similar to past from a tube/bottle. Perhaps that's too much detail there but just mentioning it JIC. Upon the lard reaching the somewhat warmed water-oil solution, it started popping in basically the same way that high-temperature oils do when water is added at frying temperatures.
What chemical/physical process is facilitating this phenomenon?