Exegesis:

blepete (cf. 8.15) ‘beware!’ ‘caution!’ ‘watch out!’ Moulton & Milligan give examples from the papyri showing that this use of the verb blepō ‘see’ was not purely Semitic, but was Greek as well.

mē tis humas planēsē ‘lest any one deceive you,’ ‘that no one lead you astray.’

planaō (cf. 12.24) in the active, as here, ‘cause to err,’ ‘lead astray,’ ‘deceive.’

Translation:

Leads you astray is equivalent to ‘deceive,’ or as in some languages ‘cause you to believe a lie.’

Quoted with permission from Bratcher, Robert G. and Nida, Eugene A. A Handbook on the Gospel of Mark. (UBS Handbook Series). New York: UBS, 1961. For this and other handbooks for translators see here .