If your "variable" has a continuous range of values, you can do the following:
Code:
Option Explicit

Private Enum aniAnimals
    [aniLow] = 3
    aniDog = 3
    aniCat = 4
    aniMouse = 5
    [anihigh] = 5
End Enum

Private Sub Text1_Change()

    If Len(Trim(Text1)) > 0 Then
        If Val(Text1) < aniLow Or Val(Text1) > anihigh Then
            MsgBox "Please enter an animal number (a value from 3 to 5)"
        Else
            MsgBox "Thanks"
        End If
    End If
End Sub