What would be the easiest way to end one’s own life if they were ever kept captive and death would be better than imprisonment?

I don’t know the specifics of the method but when I was being taught about the slave trade one of the accounts talked about a certain way that the slaves would sit that would allow them to suffocate themselves to death, the slavers would force slaves trying to kill themselves this way to get up and dance around so as to not lose “product”.