Exegesis:
hopou ean auton katalabē ‘wherever it seizes him,’ i.e. wherever the boy might be when the spirit seizes him.
hopou ean (hopou an 6.56) ‘wherever,’ ‘whatever place.’
katalambanō (only here in Mark) ‘take hold of’: with hostile intent, as here, ‘seize.’
rēssei auton kai aphrizei kai trizei tous odontas kai xērainetai ‘it throws him to the ground, and he foams at the mouth and grinds his teeth and grows rigid.’
rēssō (cf. rēgnumi 2.22) ‘throw down,’ ‘dash to the ground.’
aphrizō (9.20) ‘foam at the mouth.’
trizō (only here in the N. T.) ‘gnash,’ ‘grind,’ ‘grit.’
xērainō (cf. 3.1) ‘dry up,’ ‘wither,’ therefore (as in 3.1), ‘grow rigid,’ ‘become stiff’ (cf. Manson, Moffatt, Le Nouveau Testament. Version Synodale). This meaning of the word suits the context better than ‘waste away,’ ‘pine away’ (American Standard Version, Goodspeed, The Modern Speech New Testament, O Novo Testamento de Nosso Senhor Jesus Cristo. Revisdo Autorizada). Translator’s New Testament has ‘becomes parched.’
The other words have already been dealt with: hina ‘that’ of content, not of purpose, cf. 3.9; ekballō ‘cast out’ cf. 1.12, 34; ischuō ‘be strong,’ ‘be able’ cf. 2.17; 5.4.
Translation:
As in all expressions of demonic seizure (cf. Revised Standard Version seizes him), one must make certain of the way in which one can speak of such events in the receptor language (see 1.23). In some instances it may be necessary to speak of ‘entering into,’ ‘taking hold of him,’ or ‘being captured by.’
Dashes him down is equivalent in some languages to ‘causes him to fall down,’ especially if the demon is regarded as being within the person. However, whenever possible this strong figure should be used, but the idiom must be applicable to persons, and not exclusively to things (as has been the case in certain translations).
He may need to be changed to ‘the boy,’ since the pronominal reference may not clearly indicate the shift between the dumb spirit as the subject and the boy.
Foams may be easily translated in most languages by finding out how people describe the actions of demented persons, epileptics, or those suffering from rabies. In Southern Subanen one says literally ‘his mouth fills with bubbles.’
Becomes rigid is translatable as ‘his body becomes stiff’ (Southern Subanen) and ‘he becomes bone’ (Conob).
For cast it out see 1.34.
Were not able is translatable as ‘could not do so’ or ‘could not cast the demon out.’ In some languages one says ‘they did not have the strength to do so.’
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 .