Detect Duplicate words in sentences

This little macro detects duplicated words in sentences.
unlike Microsoft Word's grammar/spell checker which merely identifies consecutive duplicate words, this macro (and associated function) marks in RED second and subsequent occurrences of words in each sentence.
A short list of noise words is provided as a string constant; we don't mind those words being repeated.

Public Const strcIgnoreWords As String = vbTab & "and" & vbTab & "on" & vbTab & "the" & vbTab
Sub DuplicateWordsInSentences()
  Dim prg As Paragraph
  For Each prg In ActiveDocument.Paragraphs
      Dim snt As Range
      For Each snt In prg.Range.Sentences
          Call FindDupInSentence(snt)
      Next snt
  Next prg
End Sub
Function FindDupInSentence(snt As Range)
  Dim strAllWords As String
  strAllWords = vbTab
  Dim wd As Range
  For Each wd In snt.Words
      Dim strWd As String
      strWd = Trim(wd.Text)
      If Len(strWd) > 1 Then
          If InStr(1, strcIgnoreWords, vbTab & strWd & vbTab) > 0 Then ' we ignore this word
          Else
              If InStr(1, strAllWords, vbTab & strWd & vbTab) > 0 Then
                  wd.Font.Color = wdColorRed
              Else
                  strAllWords = strAllWords & strWd & vbTab
              End If
          End If
      Else ' we ignore words of length 1 character
      End If
  Next wd
End Function