Gravel was my main concern lately. I bought the largest available aquarium gravel in shop, but when i washed it and placed it in the tank, i suddenly thought it might be a problem. basically it's 5-8mm gravel. They technically can have it in mouth, but i was not sure if they could swallow a gravel as big as a prey by mistake. I mean,it seems almost impossible for them to get both prey and gravel in mouth at same time....
It would be like a human swallowing by mistake a lemon.

On land, the gravel is covered by terrrarium soil, and will get moss and other plants. The land-water connection has large rocks on it.

thanks for your help