Exegesis:

apostellousin is probably impersonal ‘they send,’ i.e. ‘(some of the Pharisees and some of the Herodians) were sent.’ It is not likely that the subject of the verb is the ‘they’ of the previous verse (which, in the Marcan context, goes back to ‘them’ in 12.1 and eventually to ‘the chief priests and the scribes and the elders’ in 11.27).

agreusōsin (only here in the N.T.) ‘they may catch,’ ‘they may take’: used in the papyri (cf. Moulton & Milligan) literally of hunting and fishing.

logō ‘in a word,’ ‘by means of a statement.’

Translation:

Herodians are ‘the henchmen of Herod’ or ‘the followers of Herod.’

To entrap him in his talk has been idiomatically rendered in Shipibo-Conibo as ‘having headed him off to catch him’ (a metaphorical expression derived from the practice of tracking down animals). In Copainalá Zoque this same expression is rendered ‘to cause him to fall because of his words’ and in Tzotzil one may say ‘to catch him because of what he said.’

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 .