You couldn't call those songs decipherable. In many of their songs during the middle or late part of the band's career, she sings gibberish (as on "Blue Bell Knoll") or Latinate scientific terms and such (as on "Echoes in a Shallow Bay").
For years journalists, fans, and even record labels tried desperately to decipher what Elizabeth Fraser might have been singing. Lyrics. One of the biggest ongoing debates about Cocteau Twins relates to the “lyrics,” or lack thereof.