Waka no ura ni shio michi kureba kata wo nami
ashibe wo sashite tazu naki wataru
When the tide rises in Waka-no-ura* bay, the tidal flats disappear, so a flock of cranes pass crying toward a reedy shore.
(*Waka-no-ura is the name of a bay in Wakayama city.)
That's a tanka (Japanese poem) composed by Yamabe no Akahito, contained in Man'yōshū. The poem is written in hentaigana, so it's understandable that your friends couldn't read it even if they are Japanese.