The Suggestion spell

[RigaMortus]

No, actually it doesn't. It only implies that the spell can significantly change perceptions if you assume that the "pool of acid" is bubbling, frothing, spilling out toxic fumes, and has a hazard label on the side. If the "pool of acid" actually looks like clear water (and a lot of acids do look like water), then it does not imply that the spell can significantly change perceptions. Since taking "a quick dip" in a pool of obvious acid is as obviously harmful as sticking a knife through your arm which is explicitly prohibited by the spell, the conclusion that makes the best sense of the text is that the pool of acid is assumed to look like water or at least not be known to be acid. Otherwise, the suggestion "pain can sometimes be pleasurable; you'd have fun if you stuck the knife into your arm and then plunged it into a vat of rubbing alcohol" would be workable.

I concur

 

[Shadowdweller]

No, actually it doesn't. It only implies that the spell can significantly change perceptions if you assume that the "pool of acid" is bubbling, frothing, spilling out toxic fumes, and has a hazard label on the side.

This DOES, however, appear to be the 'default' condition in 3.5. Or at least the toxic fumes part. From the DMG this time, under Acid Effects:

The fumes from most acids are inhaled poisons. Those who come close enough to a large body of acid to dunk a creature in it must make a DC 13 fortitude save or take 1 point of constitution damage.

Perhaps the word 'significant' was excessive on my part. Regardless of the emphasis one places on the word "significant" in previous discussions, however, there IS a perceptual change involved in this form of the spell. Otherwise it would be wrong to state that the "pool of acid is actually pure water". Because it would actually be "That (mysterious) pool of clear liquid looks inviting. A quick dip would be refreshing."

If the "pool of acid" actually looks like clear water (and a lot of acids do look like water), then it does not imply that the spell can significantly change perceptions

Which is obviously the basis for this suggestion being reasonable. HOWEVER, note that while most acids look like water (or at least aqueous solutions of the former, since for the most part they ARE water) nearly every acid capable of doing fast harm to anyone tends to have a very strong SMELL. Or at least notably caustic vapors when in large quantity.