Could it also be "Manges les friases!" ? If you (tu) is implied in an imperative statement, then could you ever use the "tu" conjugation?
The 'tu' imperative of -ER verbs and those conjugated like -ER verbs (i.e. 'tu' form ending in -es) is the present tense minus the final 's', e.g. tu manges -> mange - Read more: http://french.about.com/od/grammar/a/imperative_2.htm
The final -s is always dropped in the "tu" imperative. The imperative is a completely different conjugation - it just happens to be very similar to the imperative. :)
manger: tu mange (no -s) nous mangeons vous mangez
I've already seen a bunch of cases where this is not the case, and the "s" is kept, and I don't yet understand what the logic behind it is.
Not totally sure, but as a rule of thumb I've heard that you drop the final -s in regular verbs.
I think just because if it was mangez you would have heard the hard "è" sound at the end.
The -s is only dropped from the second person singular of -er type verbs the other verbs just use the second person singular or plural , and the nous form without the pronoun. Just watch out though there are some irregular verbs eg être -sec pers plural= étes, imperative =soyez.