If you walk from a block that is shorter than a full block to another block that is also shorter than a full block, but taller than the first, you will momentarily glitch into the original into the block you are walking onto.
1 Place a bed on the ground
2 Place an enchantment table directly next to the bed
3 Attempt to walk from the bed onto the enchantment table.
4 You will glitch down into the enchantment table, then pop back up.
~ Works with any two blocks as long as neither block is a full block, and you are going onto a block with a taller collision box