emacs -Q
C-x C-f /:/tmp/foobar.txt (it doesn't matter whether the file exists)
M-: (process-file "true")

will result in an error

Debugger entered--Lisp error: (file-missing "Setting current directory" "No such file or directory" "/:/tmp/")
  call-process("true" nil nil nil)
  apply(call-process "true" nil nil nil nil)
  process-file("true" nil nil nil)
  apply(process-file ("true" nil nil nil))
  file-name-non-special(process-file "true" nil nil nil)
  apply(file-name-non-special process-file "true" nil nil nil nil)
  process-file("true" nil nil nil)
  apply(process-file ("true" nil nil nil))
  tramp-run-real-handler(process-file ("true" nil nil nil))
  tramp-file-name-handler(process-file "true" nil nil nil)
  apply(tramp-file-name-handler process-file "true" nil nil nil nil)
  process-file("true")
  eval((process-file "true") nil)
  eval-expression((process-file "true") nil)
  funcall-interactively(eval-expression (process-file "true") nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)