Our baby is 8 month old, and he can sit by himself, flip himself, and generally twist himself whichever way he wants to reach or look at something.
But he seems to be having a block when it comes to crawling: passive tummy time is fine, but as soon as he tries to crawl, he gets frustrated very fast by the efforts: he starts shouting very loudly continuously, and it can escalate to crying. He obviously wants to move around by himself, so we feel like we shouldn't just wait.
Trying to lift him to "show" him that he can put his knees under his body make him enter "being carried mode", and putting something under his belly instead tends to make him passive. We also try showing him by crawling ourselves, but that seems to trigger mild curiosity at best :)
What can we do to get him to practice crawling, without him getting instantly frustrated ?