Yesterday, during our early morning walk, we encountered a Filipina lady, and my wife asked her how come she is always smiling. She replied 'From birth', with [t] at the end of 'birth'. My wife did not understand and asked for clarification, but the Filipina just repeated it the same way. Then my wife changed the subject. She later told me that she had heard 'bird' instead of 'birth', and she was confused about the idea of learning to smile from watching birds.
It has often been claimed that replacement of dental fricatives is not problematic in international Englishes, as so many people replace voiceless TH with [t], [s] or [f] that listeners have become accustomed to it. But this is a counter-example, where use of [t] in place of /θ/ did result in the loss of intelligibility.
