If the woman performed the halizah with a sandal that did not belong to him, or with a wooden sandal, or with the one of the left foot [which he was wearing] on his right foot, the halizah is valid. If she performed the halizah with a sandal too large [for him], in which, however, he is able to walk, or with one too small which, however, covers the greater part of his foot, Her halizah is valid. 
If [a sister-in-law] performed the halizah at night, Her halizah is valid. R. Eleazar, however, regards it as invalid. [If she performed it] with [the levir`s] left shoe, Her halizah is invalid, but R. Eleazar declares it to be valid

 יבמות 12.2
חלצה בסנדל שאינו שלו, או בסנדל של עץ, או בשל שמאל בימין-- חליצתה כשרה׃ חלצה בגדול שהוא יכול להלך בו, או בקטן שהוא חופה את רוב רגלו-- חליצתה כשרה׃ חלצה בלילה, חליצתה כשרה; רבי אליעזר פוסל׃ ובשמאל, חליצתה פסולה; ורבי אליעזר מכשיר

[If a sister-in-law] drew off [the levir`s shoe] and spat, but did not recite [the formulae], Her halizah is valid. If she recited [the formulae] and spat, but did not draw off the shoe, Her halizah is invalid. If she drew off the shoe and recited [the formulae] but did not spit, Her halizah, R. Eliezer stated, is invalid; and R. Akiba stated: Her halizah is valid. Said R. Eliezer to him: [Scripture stated], so shall be done, anything which is a deed is a sine qua non. R. Akiba, however, said to him, from this very text proof [may be adduced for my view]: so shall be done unto the man, only that which is to be done unto the man.

יבמות 12.3
חלצה ורקקה, אבל לא קראה; חליצתה כשרה׃ קראה ורקקה, אבל לא חלצה; חליצתה פסולה׃ חלצה וקראה, אבל לא רקקה-- רבי אליעזר אומר, חליצתה פסולה; רבי עקיבה אומר, חליצתה כשרה׃ אמר רבי אליעזר, ''ככה ייעשה''  (דברים כה,ט) -- דבר שהוא מעשה, מעכב; אמר לו רבי עקיבה, משם ראיה-- ''ייעשה לאיש''  (שם) , דבר שהוא מעשה באיש.