Really small bits shouldn't be a choking hazard. I think part of the gagging is getting used to the lumps and texture more than actually choking. It can be a bit unnerving hearing it though I know.

It won't be long before he is putting anything he can find on the floor into his mouth (fluff, bugs etc) too so it will come about eventually that he gets used to things in his mouth

Watermelon custard! yummo!