[foobar1962]

I assume by "lethal" you mean "highly reactive" as opposed to "poisonous". Something that really wants to give away electrons and something that really wants to gain electrons are going to really get on well, and will be really stable.

[Woshiwuja]

well i think sodium exploding in your mouth if you eat it is pretty lethal ngl

[djtango]

Is there enough water in the mouth to get sodium to explode? Probably just scalds you.

Elemental sodium in the air spontaneously oxidises to sodium hydroxide which is nasty and caustic but the hydroxide layer spontaneously forms bicarb which is comparatively harmless. At a best guess, I'm not convinced a block of sodium not swallowed is lethal... (it will be extremely harmful)

[Woshiwuja]

i think it depends on how much spit you can gather first

[djtango]

Volume of the mouth is about 150mls (half a can of coke). Maybe you have a big mouth so let's call it 180mls. That's 10 moles of water (assuming saliva is 100% water). At 0.9688gcm^-3 they're basically 1:1 and the stoichiometry is also 1. So max you can fit about 115g of sodium to 90ml of water.

If we ignore the dynamics of the explosion that seems enough to cause a maybe lethal explosion. It would also release 120dm^3 of hydrogen.

[Woshiwuja]

that sounds like a pretty big boom for a mouth to handle ngl