Question

How can methanol be harmful to human if accidentically swallowed

Answer 1

http://www.nlm.nih.gov/medlineplus/ency/article/002680.htm

Answer 2

After humans are exposed to methanol, the dangerous symptoms result when methanol is transformed into formic acid in the body; it is the formic acid that damages the central nervous system.

Answer 3

http://emedicine.medscape.com/article/1174890-overview