When your head is in Webs, Vines, Sugar Cane or a Sign, hostile mobs will not attack you or explode until you leave them. Mobs that are pursuing you before you enter any of the blocks listed above sometimes totally forget about you once you get into them.

The following mobs are affected by this:

• Zombie: Doesn't notice the player usually.
• Baby zombies/pigmen/villagers: Same as Zombie/Pigmen. Baby villager notices you.
• Skeleton: Refuses to attack while the player is inside the web
• Spider: Attempts to attack but can't.
• Silverfish: Attempts to attack but can't.
• Enderman: Attempts to attack but can't.
• Blaze: Appears to be hostile but doesn't attack. (They catch fire and fly around but don't shoot at you.)
• Slimes and Magma Cubes: Can't see you while in webs, but seems to be able to with Sugar Canes. They still don't attack you but hop rapidly as if they were chasing you.
• Creeper: If one is chasing you and you enter one of the blocks that causes the behavior, it will walk right up to you, then forget about you. If you leave the block they will notice you and try to explode.
• Cave Spider: Same as spider. Don't confuse the poison damage you take as it attacking you through the web.
• Aggressive wolves: Attempt to attack you but can't.
• Pigmen that are aggressive can sometimes get into the web and hurt you, but this doesn't happen very often. They behave like the Zombies do.
• Sheep and other animals that can be attracted/bred with wheat, seeds, carrots, etc. WILL still notice you in the web.
• Villagers appear to be affected but some still stare at you even after you entered the web.
• Baby villagers and Baby villager zombies do not notice you at all while in the webs
• Ghasts do not attempt to attack you while in the web. But unlike skeletons, they shoot exploding fireballs so they can destroy the web if you peek out of it to get their attention.
• Guardians will not attempt to shoot through non-solid blocks

The screenshots below show multiple different mobs trying to get me when I'm in the webs. Note that the spiders seemed to notice me but still didn't attack me.

The screenshot with 2 webs in it is the web setup I use to reproduce this bug. It also works with only the top web.

Note: Yes, I understand that this bug reporter is not for modded clients, as you might have noticed the coordinates in the top left corner of the majority of the screenshots, but this has ALSO been tested in Vanilla Minecraft (Deleted and re-installed the ENTIRE FOLDER!). It was easier to not have to use a different Minecraft every time I took a picture because I was playing at the same time and didn't feel like switching out every 5 minutes.