From Twelfth Night (3.1), a unique image here of the high-strung and restless nature of a constantly exercised wit :
This fellow is wise enough to play the fool;
And to do that well craves a kind of wit:
He must observe their mood on whom he jests,
The quality of persons, and the time,
And, like the haggard, check at every feather
That comes before his eye. This is a practice
As full of labour as a wise man’s art
For folly that he wisely shows is fit;
But wise men, folly-fallen, quite taint their wit.
A haggard is a female hawk caught as an adult and difficult to train. Check is a more difficult word and since we should all take any available chance to improve our knowledge of technical hawking and falconry terms, I give the full OED entry below for definitions 6A and 6B:
a. to check at the fist: to refuse to come to, recoil from, ‘shy’ at the fist.
a1529 J. Skelton Why come ye nat to Courte (?1545) 732 Till he cheked at the fist.
1557 Earl of Surrey et al. Songes & Sonettes (new ed.) f. 94v The hauke may check, that now comes fair to fiist.
1618 S. Latham New & 2nd Bk. Falconrie xi. 37 She will neuer vnderstand what it is to checke at the fist: but..wil proue a certaine and bold commer.
b. See quot. 1615, 1852; and cf. check n.1 6a.
Sir Walter Scott’s archaic use appears to be erroneous, since one falcon does not ‘check’ at another, and Marmion would not figure himself as ‘base game’ crossing the path of nobler quarry.
1615 S. Latham Falconry (new ed.) Words of Art expl. Checke, or to kill Checke, is when Crows, Rooks, Pies, or other birds comming in the view of the Hawke, she forsaketh her naturall flight to flie at them.
a1616 W. Shakespeare Twelfth Night (1623) iii. i. 63 Like the Haggard, checke at euery Feather That comes before his eye.
1808 W. Scott Marmion i. vi. 28 E’en such a falcon, on his shield. The golden legend bore aright, ‘Who checks at me, to death is dight.’
1852 R. F. Burton Falconry in Valley of Indus iii. 31 She ‘checked’ first at one bird, then at the other. [Note] To ‘check’ is to forsake the quarry, and fly at any chance bird that crosses the path.
The 1852 gloss – “to ‘check’ is to forsake the quarry, and fly at any chance bird that crosses the path” – is a very pretty capturing of wit’s hyperactive and undisciplined (but not ineffective) response to the things around it.