Essentially if you walk at a block it should stop you walking inside it.
If the block is one up from the ground (about face height) and there is no block under it then you can walk inside the block and suffocate. 

Here is a video of me doing it:

https://youtu.be/gvihbVB0jLM

To do this: place any block one block up from the ground. Walk at it. You will walk inside the block instead of stop at the block.