1)In Sura 34:50, Muhammad is commanded to say the following:
Say: ‘If I go astray, I go astray only to my own loss; if I am guided, it is by what my Lord reveals to me. He is All-hearing, Ever-nigh.’ Arberry
Say: "If (even) I go astray, I shall stray only to my own loss. But if I remain guided, it is because of the Inspiration of my Lord to me. Truly, He is AllHearer, Ever Near (to all things)." Hilali & Khan
The error in this verse should be obvious to anyone pondering this statement for a little bit. The issue here is not whether, objectively, Muhammad went astray or was guided; Muslims and non-Muslims will continue to disagree about that. This verse is logically wrong, independent of whether Muhammad was guided or not.
2)The Qur'an makes the following statements regarding the food that unbelievers will have in hell:
No food will there be for them but a bitter Dhari S. 88:6 Y. Ali
Nor hath he any food except the foul pus from the washing of wounds, S. 69:36 Y. Ali
3)The very first revelation starts out with providing an ingredient for contradiction:
In the name of thy Lord and Cherisher, who created -
created man, out of a mere clot of congealed blood.
-- Sura 96:1-2
Apart from the fact that "a mere blood clot" is scientifically wrong, let us see what further ideas the Qur'an presents on how God creates human beings.
It is he who has created man from water
-- Sura 25:54
And God has created every living creature from water.
-- Sura 24:45
We created man from sounding clay,
from mud moulded into shape.
-- Sura 15:26
Amongst his signs is this,
that he created you from dust.
-- Sura 30:20
Blood clot? water? clay? dust? The Qur'an doesn't really seem all that sure what God used and seems to imply that He took just anything he could get his hands on. But this is still not all in this confusion:
God createth what He willeth:
When he hath decreed a plan,
He but saith to it, "Be," and it is!
-- Sura 3:47
and many more...