Whether the circumstances of a given case present grounds sufficient to warrant removal of a juror is a question entrusted to the trial court's sound discretion, and the court's finding on that issue will be sustained if supported by substantial evidence. (People v. Johnson, supra, 6 Cal. 4th 1, 21; People v. Burgener (1986) 41 Cal. 3d 505, 519-520, 224 Cal. Rptr. 112, 714 P.2d 1251, disapproved on another point in People v. Reyes (1998) 19 Cal. 4th 229, 231, 236-239, 961 P.2d 984.) The court's discretion "is limited, however, in that the juror's inability to perform the functions of a juror must appear in the record as a demonstrable reality. (People v. Collins, supra, 17 Cal. 3d at p. 696; People v. Thomas[, supra,] 218 Cal. App. 3d 1477, 1484 [267 Cal. Rptr. 865].)" ( People v. Green, supra, 31 Cal. App. 4th 1001, 1011-1012; see People v. Johnson, supra, 6 Cal. 4th at p. 21, quoting People v. Compton (1971) 6 Cal. 3d 55, 60, 98 Cal. Rptr. 217, 490 P.2d 537; People v. Roberts (1992) 2 Cal. 4th 271, 325, 826 P.2d 274 [court's discretion "not unbounded"].)