Why are there grids on every entity
You have activated a F3 command: F3 + B. It shows the hitboxes of entities. To disable it, press F3 + B again(or add the Fn key if it doesn't work).
F3+B : Toggle visibility of hitboxes of entities. It also shows which direction entities are looking in using a blue line.
Source: http://minecraft.gamepedia.com/Debug_screen