Pigs

The very first passive mob added to Minecraft was the pig.

When struck by lightning, pigs will become zombified piglins.

The pig texture has six nipples, while real pigs usually have eight. However, in-game pigs also feature toes, just like real pigs. 

In earlier versions of the game, pigs would drop up to two mushrooms. Now, pigs usually drop up to three raw porkchops, but pigs that are on fire drop cooked porkchops instead. The porkchop was introduced to the game in 2010, with its raw variant currently restoring 3 saturation points (1.5 drumsticks) and the cooked variant restoring 8 saturation points (4 drumsticks). Raw porkchops have zero chances of giving the player the Hunger effect, the in-game version of food poisoning.

Pigs can be bred with carrots, potatoes, and beetroot; baby pigs will also grow faster when fed any of the three. However, when pigs were first added to the game, they could only be bred with wheat. Holding a carrot on a stick will attract nearby pigs just like holding a carrot, potato, or beetroot.

Saddles can be put on pigs, but they can only be steered with a carrot on a stick; the ability to ride a baby pig was removed early on in the game. The player can ride pigs up ladders. Riding a pig in a minecart will allow the player to travel on normal rails at the speed of powered rails. 

Players can unlock the When Pigs Fly achievement on Bedrock Edition by falling for at least five blocks while riding a pig; this achievement was removed from Java Edition.

The heads of baby and adult pigs are the same size.

When mob spawners were first included in the game, they featured a model of the pig instead of a model of the mob being spawned.

The creeper came from a failed pig design.

Pigmen were supposed to populate villages until villagers were introduced.

Seagrass

Areas surrounded by seagrass are less likely to have hostile mobs spawn because mobs cannot naturally spawn on blocks inhabited by seagrass.

Seagrass can be used on composters.

Turtles are bred with seagrass and baby turtles will reach maturity sooner when fed seagrass.

Seagrass naturally generates on underwater gravel but will also generate on nearby dirt and sand if bonemeal is used on the original block with seagrass. Seagrass can only be harvested with shears, and once harvested, can be placed on other blocks.

Seagrass cannot be placed on dry land and will be destroyed if it loses access to its water source; it cannot be placed on blocks that are only partially submerged in water.

Lava cannot flow into seagrass; it will just flow over or around the seagrass, instead. 

Bonus Fact

Turtles can drop a bowl when struck by lightning.

Citations:

YouTube. (2016). Minecraft: 10 Things You Didn’t Know About the Pig . YouTube. Retrieved September 23, 2021, from https://www.youtube.com/watch?v=xiOzIU8aluI. 

YouTube. (2016). ✔ Minecraft: 20 Things You Didn’t Know About the Pig. YouTube. Retrieved September 26, 2021, from https://www.youtube.com/watch?v=1oRUm8_xBi8. 

Hansen, J. (2021, August 29). What do pigs eat in Minecraft? Gamepur. Retrieved September 23, 2021, from https://www.gamepur.com/guides/what-do-pigs-eat-in-minecraft. 

Geere, D. (2020, February 13). Taking inventory: Porkchop. Minecraft.net. Retrieved September 23, 2021, from https://www.minecraft.net/en-us/article/taking-inventory–porkchop#:~:text=OINK.,pigs%20are%20straight%2Dup%20adorable.&text=They%20were%20added%20in%20February,half%20points%20of%20hunger%20instead. 

Bair, H. (2021, May 24). Top 5 uses of seagrass in Minecraft. Sports news. Retrieved September 23, 2021, from https://www.sportskeeda.com/minecraft/top-5-uses-seagrass-minecraft. 

YouTube. (2021). Why do turtles drop Bowls???? Minecraft. YouTube. Retrieved September 23, 2021, from https://www.youtube.com/watch?v=GSBErV1tHq8. 

Personal experience (and experiments!).