If you receive any damage at all, from an entity of any kind, such as a Mob, or another player, it will crash your client in Multi-Player.
Environment
Windows 7 Ultimate 64-Bit.
4GB DDR2 Ram.
Intel Pentium 2.6GHz Dual-Core.
BFG Tech Nvidia GeForce 9600GT OverClocked Graphics Card.
Java 7 Update 51.
Duplicate of MC-45496 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.