It depends on dialect but it usually happens when you have the combination of letters/cluster "rs". It can also happen when you have "rs" between two words like in "Vær så snill". Basically "rs" sounds kind of like like"sh".
It's a retroflex sound. Here you have examples and explanation on that and more retroflex sounds:
When asked to translate into norwegian, "prøve" was accepted in place of "forsøke". But when translating into english "try" was not accepted. Is there something I am missing, or does this need flagged? Thanks in advance! :)
.... Never mind.... just noticed I somehow typed "we" instead of "he" also. Oops!