Theophilus Thistle by Unknown Author

Theophilus Thistle, the Thistle Sifter,
Sifted a sieve of unsifted thistles.
If Theophilus Thistle, the Thistle Sifter,
Sifted a sieve of unsifted thistles,
Where is the sieve of un-sifted thistles
Theophilus Thistle, the Thistle Sifter, sifted?