At first glance you may think “Contents Inflammable” should be “Contents Flammable”…. but according to Oxford English Dictionary:

Flammable means easily set on fire (link)

Inflammable means easily set on fire AGAIN 😛 (link)

The words inflammable and flammable both have the same meaning, ‘easily set on fire’. This might seem surprising, given that the prefix in- normally has a negative meaning (as in indirect and insufficient), and so it might be expected that inflammable would mean the opposite of flammable, i.e. ‘not easily set on fire’. In fact, inflammable is formed using a different Latin prefix in-, which has the meaning ‘into’ and here has the effect of intensifying the meaning of the word in English. Flammable is a far commoner word than inflammable and carries less risk of confusion

Isn’t English language fun? 😉