If you are under the effects of a Silence spell, you cannot cast spells. This is because you make no noise, and speaking is required to cast a magical spell. But the rest of your body makes no noise either, and as such you are now silent. Your footfalls are silent. You move like a silent film, creepy and weightless. You can only “speak” through pantomime, but you gain a great bonus to your stealth abilities. Either roll with advantage while sneaking or treat the Rogue skill of “move silently” at 100%
Ring of Silence
If you wear this ring, you are silenced. You cannot speak or make any noise, though you do become incredibly stealthy. If your level + charisma moidifer is under this item's Ego score, it is cursed when you put it on and you cannot take it off without a curse removal spell or a Sage to cure it.
Everyone knows what poison does. It slowly drains your hit points unless you take an antidote, or outright kills you if it's a save vs death poison. As many people have stated, animals like snakes and spiders aren't technically poisonous, they are venomous, but the effect is called poison when it deals damage to you either way. But what if being bitten by something venomous makes you poisonous?
If an enemy bites you while you are suffering from a poison (made your save vs death poison less then one turn ago, OR you are suffering from a damage over time poison that has not yet been nullifed), the enemy who bit you must make a save vs poison or also be poisoned from tasting your infected blood. They get a +2 to the save for the second hand effect and weakening of the poison from it being in your blood, but if they fail the save they suffer from the same damage and effect the poison dealt to you. This means that getting poisoned and wading into battle with no armor against animals or monsters that perform bite attacks may not exactly be a valid tactic, but it could deal some damage back to your foes. Also, a character who is immune to poison may or may not be able to spread poison in this way; at the very least a character with an 18 Constitution may decide to drink some minor poison before fighting some blood sucking vampire-bats or something.
Level Drain = Unholy
In some games and settings, leveling up may literally be equivalent to gaining some god of godly Numen. Perhaps experience points are some kind of codified life energy, or literally gaining in some divine tract; as in some games the end-game for player characters may be to ascend to Godhood.
However, it could be thought that the concept of undead level drain (who coincidentally are also the enemies of the Gods, at least the Good Gods in most fantasy settings) is similar to being drained of this holy presence. But it could even be thought of as a form of infectious evil or UN-divinity. In the same way a man with a fever can touch you and you can feel just a fraction of his heat, a mortal who is drained of their levels can be anathema to the divine. You are still suffering more then the divine, but there is always the taint.
If you are suffering from at least one level of level drain, you can desecrate alters or holy items. The chance of success is X in 6, where X is the number of levels drained. It could be said that being level drained acts as a shield against the divine; perhaps even the followers of Gods you fight against will fail their smiting spells or lose their blessings if you touch them. You are like the opposite of clerical magic. Of course, evil gods who work with the undead maybe are either unaffected by this property, (such as their “numen” or godly essence is the opposite of life, in a sense, so level drain or negative energy is their primary energy?) or it is just that mortals who are highly level drained can desecrate and act as black holes for holy energy. There is no guarantee that offending the Gods in this manner will get you banished from their temples; or perhaps those suffering from one or more levels of level drain can be turned as undead; all the unclean ones are banished, even those who are still alive.