Technical religious question

A few religions have things that the followers are forbidden to consume. Pork, alcohol, shellfish etc.

Now is the act of conciously choosing to eat/drink the offending article the sin or is it a sin to consume them without knowledge?

For example if someone gave a muslim pork but didn't tell him, or spiked his drink with alcohol.

If, as seems sensible, it is only a sin if eaten conciously then surely the offending foodstuff isn't, in itself, sinful. Eating it is but not eating it isn't.

From this you might begin to question what it is about pork, whilst as proven above not inherently sinful, becomes sinful if eating conciously.

If it is sinful either way then it seems a might unfair. Especially considering that mouthwash (most brands) is 11% alcohol!