A creature can be dealt an amount of damage greater than its toughness. For example, if Barbed Servitor is dealt 3 damage, its last ability causes the target opponent to lose 3 life.

If a creature is already suspected, suspecting it again won't have any effect.

There's no limit to the number of creatures that can be suspected simultaneously. Suspecting a new creature doesn't cause other creatures to stop being suspected.

If a suspected creature loses all abilities, it will lose menace and "This creature can't block", but it won't stop being suspected.

If your life total is brought to 0 or less at the same time that Barbed Servitor is dealt damage, you lose the game before its last ability goes on the stack.

When an effect suspects a creature, it becomes suspected. It gains menace and "This creature can't block" for as long as it's suspected. It stays suspected until it leaves the battlefield or another effect causes it to no longer be suspected.

Being suspected isn't a copiable value. If a permanent becomes a copy of a suspected creature, it won't be suspected.