21 The conjunction אִם (’im) introduces clauses that are conditional or concessive. With the imperfect verb in the protasis it indicates what is possible in the present or future. See §159.q).
22 The wicked person holds on to evil as long as he can, savoring the taste or the pleasure of it.
23 Heb “in the middle of his palate.”
24 The perfect verb in the apodosis might express the suddenness of the change (see S. R. Driver, Tenses in Hebrew, 204), or it might be a constative perfect looking at the action as a whole without reference to inception, progress, or completion (see §30.1d). The Niphal perfect simply means “is turned” or “turns”; “sour is supplied in the translation to clarify what is meant.
25 The word is “in his loins” or “within him.” Some translate more specifically “bowels.”
26 Some commentators suggest that the ancients believed that serpents secreted poison in the gall bladder, or that the poison came from the gall bladder of serpents. In any case, there is poison (from the root “bitter”) in the system of the wicked person; it may simply be saying it is that type of poison.

In other versions

“Though evil is sweet in his mouth,

though he hides it under his tongue,

though he is loath to let it go

and holds it in his mouth,

yet his food is turned in his stomach;

it is the venom of cobras within him.

“Though evil is sweet in his mouth

and he hides it under his tongue,

though he cannot bear to let it go

and lets it linger in his mouth,

yet his food will turn sour in his stomach;

it will become the venom of serpents within him.

Though evil tastes sweet in his mouth

and he conceals it under his tongue,

though he cherishes it and will not let it go

but keeps it in his mouth,

yet the food in his stomach turns

into cobras’ venom inside him.

“They enjoyed the sweet taste of wickedness,

letting it melt under their tongue.

They savored it,

holding it long in their mouths.

But suddenly the food in their bellies turns sour,

a poisonous venom in their stomach.

“Though wickedness tastes sweet in his mouth,

and he hides it under his tongue,

though he spares it and does not let it go

and holds it back in the midst of his palate,

in his bowels his food is turned,

the venom of horned vipers is within him.

Though wickedness be sweet in his mouth,

Though he hide it under his tongue;

Though he spare it, and forsake it not;

But keep it still within his mouth:

Yet his meat in his bowels is turned,

It is the gall of asps within him.

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