I think it is a tongue twister designed for observation of pronunciation. I read Edith Skinner's "Speaking with Distinction" and there are a lot of similar tong

I think it is a tongue twister designed for observation of pronunciation. I read Edith Skinner's "Speaking with Distinction" and there are a lot of similar tongue twisters for practicing vowels and consonants clusters. Also you can find out a lot of old tongue twisters for English in elocution textbooks in 19th century from archive.org..