If two witches would watch two watches, which witch would watch which watch?

Did you know that tongue twisters like the one in the title are a very tough task

 for our transcranial direct current stimulation? 

Yes, they are, which means that practising them is a very good way

 of stimulating the language function in our brain!

Therefore... which witch is which?

Enjoy a very spooky and witchy Halloween tonight!