I have a frog couple in Essex Ct and they talk every night for hours. I think one is in my neighbor’s stagnant swimming pool and the other is across my muddy cove. The first one trills and the second one answers a major 3rd lower. One night there was no answer for the first one so I answered. He answered back and we talked for a while. I went to my piano and figured out they are talking in G major: D (the dominant) to the answer in B (the 3rd), which is such beautiful harmony. Occasionally, if the calling frog doesn’t get an answer, he will sing E to F# (which is the 5th to the 7th of the scale; in music this note is searching for home). How amazing is this!!