It would be helpful to do an introductory activity with carpet tiles or large squares of cardboard, so that the children understand the idea of making a snake from squares, and have the opportunity to start using relevant language. Words such as up, down, across, left, right, same and different are likely to be used to describe and compare the snakes.
It is an excellent opportunity to get the children to record the different snakes that they make, either by freehand drawing or colouring boxes on grid paper. This adds to the spatial thinking required as it not only develops the idea of a Plan View, but can also lead to a discussion about rotations and mirror images. If snakes that rear up from the table are part of the investigation, the children will have to think of a way to show draw this third dimension in their drawings.
Make the most of the children's recorded arrangements by having them cut up their paper so that the drawings can by grouped and sequenced in various ways. This will prompt further discussion as they explain their groupings, and perhaps uncover some patterns. It might also prompt the discovery of more possibilities.
Collectively, the whole class may establish that they have found all the arrangements, or more able children might pursue this goal themselves. An obvious extension is to investigate snakes made from 6 or more cubes, though this would require a systematic approach if all possibilities were being sought.