1 Dropping of the lower jaw
The lower jaw of the other person for whom the surprise is arranged for might drop.
2 Raised eyebrows
If the surprise is big enough, the other person might raise their eyebrows and even touch them. (See Why do people touch their eyebrows while speaking?)
3 Jumping forward in a chair
The person might jump ahead in a chair while they are being pleased with a marvelous surprise.
4 The eyes might open
The person will widen their eyes according to the surprise they have got. The bigger the suspire is, the widen the eyes they might open.
5 Lips move slightly upwards
The edges of their lips may move upwards as soon as they get the surprise.
6 Raised upper lids
The upper lids of the person might be raised for the surprise they have been gratified with.
7 The person might stay still for seconds
It may also happen that a person will not be able to believe that the surprise is meant for them, due to which they are astonished and left speechless. This makes them stand still for a moment and do not do any actions for a few seconds. (See the body language of anxiety)