Yesterday was so lovely that we stopped for lunch in the park.
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But you will probably have heard -
Yesterday wus'o lovely tha we stop f'lunch in the park
This is because fast, natural speech in English often connects words, joins sounds and even omits sounds completely.
-Where there are 2 S together, the sound becomes a single S - was so becomes wus'o.
-The final t in that is usually not sounded in fast speech, becoming tha.
-The 'ed' ending in stopped  is sometimes difficult to say smoothly and so is omitted, this then becomes stop.
-When we speak quickly, the word for becomes shorter, so you only hear the first letter f.