问OnKey和SendKeys开始递归循环，为什么？

EN

Sub LetterPress(B as String)
If Application.ActiveCell.Row = 3 And Application.ActiveCell.Column = 5 And Application.ActiveSheet.Name = "Search" And Not IsNumeric(B) Then
    Call Search1(B)
Else
    Application.SendKeys B       'This line starts a recursive loop
End if                                                      

Sub LetterPress(B as String)
If Application.ActiveCell.Row = 3 And Application.ActiveCell.Column = 5 And Application.ActiveSheet.Name = "Search" And Not IsNumeric(B) Then
    Call Search1(B)
Else
    Application.OnKey B          'Reset Application.OnKey so a recursive loop doesn't start. This line works.
    Application.SendKeys B       'Send the string B (a letter). This works too.
    Application.OnKey B, "'LetterPress """ & B & """'"      'Assign whatever is in string variable B back to the 
End if                                                      'macro, with it self as the parameter. 
                                                            'This line somehow triggers B and starts the 
                                                            'recursive loop.