The Jinn exists in the form of a spirit, and the body of a human is permeable; therefore, the Jinn is able to enter the body of a human through any place he/she wants. The evidence for this is Allah's Verse:
وَخَلَقَ الْجَانَّ مِن مَّارِجٍ مِّن نَّارٍ ﴿١٥﴾
He created the Jinn from a fusion of fire. [Surah al-Rahman, verse 15]
Ibn `Abbas (RA) said: "From the fusion of fire; and the fusion of fire is the hot wind coming out from fire". When the Jinn enters the body of a human, it heads directly for the brain, where it can affect any organ of the body from that central position. Medical research has proved that possessed people have some strange vibrations in their brains; and many Jinn have informed me that they do indeed settle in the brain.
What does this bring up for you today?