The floating basket Moses is in during the beginning of the movie bounces in the water when the lid is closed which makes sense, but when the lid is open and you can see baby Moses it is still. This was most likely supported from the bottom because of weight or safety reasons.
Not surprising that the basket was suppported, baby Moses was played by Charleton Heston's son after all. Rather clever having his son play Moses as a baby. Really keeps it all in the family.