Where has the mustard gone?

I made this illustration based on a scene from Terry Pratchett's book "Wintersmith". In her own grave, the spirit of Miss Treason pulled out the spirit of her samdwich, in front of Death and Tiffany Aching.

As if to hide her ghostly embarrassment, she plunged her hand into her pocket and pulled out the spirit of the ham sandwich.

“Ah, it worked,” she said. “I know I—where has the mustard gone?”