Definition I found for Instrumental: 'An instrumental or instrumental song is music normally without any vocals, although it might include some inarticulate vocals, such as shouted backup vocals ...'
So a primal scream expressing emotion or a word or two is acceptable if not overdone.
Some artists have included notes describing the inspiration for their songs.
The artists' notes can be seen in a new tab.
Steve Frawley: 'Water'.
Song I4 Water
Song I3 Peter Morley: 'Night Owl'
Song I6 Billy Neal 'Something She Said'
Here is 'Something She Said'